Steps to reproduce

1. run attached code with 7.0.6.FL.20150713-Eval (or 7.0.6.FL.20150708-Eval, 7.0.6.FL.20150709-Eval) under Servlet 3 comet server push (default)
2. visit notifier.zul

Actual result

The busy message on the inner component cannot be cleared. About 80%, the issue happens.

Debug information

• when the issue happens, comet request is pending
  
• in 7.0.5, first busy message cannot be cleared under Servlet 3 comet server push. If we change to org.zkoss.zkex.ui.comet.CometServerPush, the issue never happen.
  
• Might relate to ZK-2747