SpigotCore_Main/src/de/steamwar/inventory/SWAnvilInv.java

@@ -72,10 +72,12 @@ public class SWAnvilInv {
     }
 
     public void addCloseCallback(Runnable callback) {
+        player.setLevel(0);
         builder.onClose(p -> callback.run());
     }
 
     public void open() {
+        player.setLevel(1);
         builder.open(player);
     }