popup a menu in floater

Hi

I use PopupMenu object to pop up a menu in floater, like following

var m = new PopupMenu();

a.addItem("menuitem1");

var response = m.popup();

User click "menuitem1", the response  is "menuitem1".

It's OK on windows, but it's unstable on Mac.

The response is often a empty string. If you add a alert before "var response = m.popup();", it's OK.

Does anyone have the solution for this issue?

Thanks

Simon