diff --git a/src/main/java/com/garbagemule/MobArena/commands/Commands.java b/src/main/java/com/garbagemule/MobArena/commands/Commands.java
index 46fc4f6..665d13b 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/Commands.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/Commands.java
@@ -1,7 +1,9 @@
 package com.garbagemule.MobArena.commands;
 
 import java.util.List;
+import java.util.UUID;
 
+import org.bukkit.Bukkit;
 import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Player;
 
@@ -13,6 +15,24 @@ import com.garbagemule.MobArena.util.TextUtils;
 
 public class Commands
 {
+    /**
+     * Unwrap the given CommandSender reference, in case it is a proxy.
+     * <p>
+     * Because plugins like CommandSigns use horrible proxy hacks to do what
+     * they need to do, a Player reference is not necessarily a real Player,
+     * and using that reference brings MobArena into an inconsistent state.
+     * <p>
+     * The method returns the "real" Player reference by making a UUID lookup.
+     *
+     * @param sender a CommandSender reference, possibly a proxy, non-null
+     * @return the real Player reference, possibly the same as the argument
+     */
+    public static Player unwrap(CommandSender sender) {
+        Player proxy = (Player) sender;
+        UUID id = proxy.getUniqueId();
+        return Bukkit.getPlayer(id);
+    }
+
     public static boolean isPlayer(CommandSender sender) {
         return (sender instanceof Player);
     }
diff --git a/src/main/java/com/garbagemule/MobArena/commands/setup/AddArenaCommand.java b/src/main/java/com/garbagemule/MobArena/commands/setup/AddArenaCommand.java
index 3e649b2..3af6b52 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/setup/AddArenaCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/setup/AddArenaCommand.java
@@ -27,8 +27,8 @@ public class AddArenaCommand implements Command
         // Require an arena name
         if (args.length != 1) return false;
         
-        // Cast the sender.
-        Player p = (Player) sender;
+        // Unwrap the sender.
+        Player p = Commands.unwrap(sender);
         
         Arena arena = am.getArenaWithName(args[0]);
         if (arena != null) {
diff --git a/src/main/java/com/garbagemule/MobArena/commands/setup/AutoGenerateCommand.java b/src/main/java/com/garbagemule/MobArena/commands/setup/AutoGenerateCommand.java
index f881af6..bc49e79 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/setup/AutoGenerateCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/setup/AutoGenerateCommand.java
@@ -27,8 +27,8 @@ public class AutoGenerateCommand implements Command
         // Require an arena name
         if (args.length != 1) return false;
         
-        // Cast the sender.
-        Player p = (Player) sender;
+        // Unwrap the sender.
+        Player p = Commands.unwrap(sender);
         
         // Check if arena already exists.
         Arena arena = am.getArenaWithName(args[0]);
diff --git a/src/main/java/com/garbagemule/MobArena/commands/setup/CheckSpawnsCommand.java b/src/main/java/com/garbagemule/MobArena/commands/setup/CheckSpawnsCommand.java
index e0638d6..4361a5e 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/setup/CheckSpawnsCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/setup/CheckSpawnsCommand.java
@@ -46,7 +46,7 @@ public class CheckSpawnsCommand implements Command
             Messenger.tell(sender, "There are no spawnpoints in the selected arena.");
             return true;
         }
-        Player p = (Player) sender;
+        Player p = Commands.unwrap(sender);
         arena.getRegion().checkSpawns(p);
         return true;
     }
diff --git a/src/main/java/com/garbagemule/MobArena/commands/setup/ClassChestCommand.java b/src/main/java/com/garbagemule/MobArena/commands/setup/ClassChestCommand.java
index 6743690..d94b76a 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/setup/ClassChestCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/setup/ClassChestCommand.java
@@ -40,7 +40,7 @@ public class ClassChestCommand implements Command {
             return true;
         }
 
-        Player p = (Player) sender;
+        Player p = Commands.unwrap(sender);
         Block b = p.getTargetBlock((Set<Material>) null, 10);
 
         switch (b.getType()) {
diff --git a/src/main/java/com/garbagemule/MobArena/commands/setup/SetClassCommand.java b/src/main/java/com/garbagemule/MobArena/commands/setup/SetClassCommand.java
index df2f439..604e824 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/setup/SetClassCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/setup/SetClassCommand.java
@@ -31,8 +31,8 @@ public class SetClassCommand implements Command
         String arg1 = (args.length > 0 ? args[0] : "");
         String arg2 = (args.length > 1 ? args[1] : "");
         
-        // Cast the sender.
-        Player p = (Player) sender;
+        // Unwrap the sender.
+        Player p = Commands.unwrap(sender);
         
         // Check if we're overwriting.
         boolean safe = arg1.equals("safe");
diff --git a/src/main/java/com/garbagemule/MobArena/commands/setup/SetupCommand.java b/src/main/java/com/garbagemule/MobArena/commands/setup/SetupCommand.java
index d87ac2d..e78b78e 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/setup/SetupCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/setup/SetupCommand.java
@@ -63,7 +63,7 @@ public class SetupCommand implements Command, Listener {
                 return true;
             }
         }
-        Player player = (Player) sender;
+        Player player = Commands.unwrap(sender);
 
         // Create the setup object
         Setup setup = new Setup(player, arena);
diff --git a/src/main/java/com/garbagemule/MobArena/commands/user/ArenaListCommand.java b/src/main/java/com/garbagemule/MobArena/commands/user/ArenaListCommand.java
index 993bfa8..95caa50 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/user/ArenaListCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/user/ArenaListCommand.java
@@ -24,7 +24,7 @@ public class ArenaListCommand implements Command
         List<Arena> arenas;
         
         if (Commands.isPlayer(sender)) {
-            Player p = (Player) sender;
+            Player p = Commands.unwrap(sender);
             arenas = am.getPermittedArenas(p); 
         } else {
             arenas = am.getArenas();
diff --git a/src/main/java/com/garbagemule/MobArena/commands/user/JoinCommand.java b/src/main/java/com/garbagemule/MobArena/commands/user/JoinCommand.java
index f7b83a2..ddcd1bf 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/user/JoinCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/user/JoinCommand.java
@@ -24,8 +24,8 @@ public class JoinCommand implements Command
             return true;
         }
         
-        // Cast the sender, grab the argument, if any.
-        Player p    = (Player) sender;
+        // Unwrap the sender, grab the argument, if any.
+        Player p    = Commands.unwrap(sender);
         String arg1 = (args.length > 0 ? args[0] : null);
         
         // Run some rough sanity checks, and grab the arena to join.
diff --git a/src/main/java/com/garbagemule/MobArena/commands/user/LeaveCommand.java b/src/main/java/com/garbagemule/MobArena/commands/user/LeaveCommand.java
index c89673b..f34449d 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/user/LeaveCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/user/LeaveCommand.java
@@ -24,8 +24,8 @@ public class LeaveCommand implements Command
             return true;
         }
         
-        // Cast the sender.
-        Player p = (Player) sender;
+        // Unwrap the sender.
+        Player p = Commands.unwrap(sender);
 
         Arena arena = am.getArenaWithPlayer(p);  
         if (arena == null) {
diff --git a/src/main/java/com/garbagemule/MobArena/commands/user/NotReadyCommand.java b/src/main/java/com/garbagemule/MobArena/commands/user/NotReadyCommand.java
index 9fa0e69..743e248 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/user/NotReadyCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/user/NotReadyCommand.java
@@ -32,7 +32,7 @@ public class NotReadyCommand implements Command
                 return false;
             }
         } else if (Commands.isPlayer(sender)) {
-            Player p = (Player) sender;
+            Player p = Commands.unwrap(sender);
             arena = am.getArenaWithPlayer(p);
             
             if (arena == null) {
diff --git a/src/main/java/com/garbagemule/MobArena/commands/user/PickClassCommand.java b/src/main/java/com/garbagemule/MobArena/commands/user/PickClassCommand.java
index b794f14..54e5af1 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/user/PickClassCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/user/PickClassCommand.java
@@ -36,8 +36,8 @@ public class PickClassCommand implements Command
         // Require a class name
         if (args.length != 1) return false;
         
-        // Cast the sender
-        Player p = (Player) sender;
+        // Unwrap the sender
+        Player p = Commands.unwrap(sender);
 
         // Make sure the player is in an arena
         Arena arena = am.getArenaWithPlayer(p);
diff --git a/src/main/java/com/garbagemule/MobArena/commands/user/SpecCommand.java b/src/main/java/com/garbagemule/MobArena/commands/user/SpecCommand.java
index fabedd6..daf98c3 100644
--- a/src/main/java/com/garbagemule/MobArena/commands/user/SpecCommand.java
+++ b/src/main/java/com/garbagemule/MobArena/commands/user/SpecCommand.java
@@ -24,8 +24,8 @@ public class SpecCommand implements Command
             return false;
         }
         
-        // Cast the sender, grab the argument, if any.
-        Player p    = (Player) sender;
+        // Unwrap the sender, grab the argument, if any.
+        Player p    = Commands.unwrap(sender);
         String arg1 = (args.length > 0 ? args[0] : null);
         
         // Run some rough sanity checks, and grab the arena to spec.