Disconnected means disconnected.

src/main/java/net/minecraft/server/NetServerHandler.java

@@ -657,6 +657,7 @@ public class NetServerHandler extends NetHandler implements ICommandListener {
     }
 
     public void a(Packet packet) {
+        if (this.disconnected) return; // CraftBukkit
         a.warning(this.getClass() + " wasn\'t prepared to deal with a " + packet.getClass());
         this.disconnect("Protocol error, unexpected packet");
     }