Steps to Reproduce

<toolbarbutton id="btn" label="Test" tooltip="pp"/>
<popup id="pp">
<checkbox onClick="alert(0);" onCheck="alert(1);"/>
</popup>

(Other widgets like Textbox etc. have the same problem)
Hover the toolbarbutton to show the popup with the checkbox. Click.

Current Result

No messagebox.

Expected Result

Two messageboxes.

Workaround

Replace Popup by Div and position via Javascript; quite ugly