Added missing check

Author: photonstorm

src/physics/arcade/World.js

@@ -2002,9 +2002,9 @@ var World = new Class({
             {
                 bodyB = results[i];
 
-                if (bodyA === bodyB)
+                if (bodyA === bodyB || !group.contains(bodyB.gameObject))
                 {
-                    //  Skip if comparing against itself
+                    //  Skip if comparing against itself, or if bodyB isn't actually part of the Group
                     continue;
                 }