The onClick event in flash isn't working with IE8 and IE9. However it works with Firefox and Eclipse embedded browser.
In IE9 a click on the right side near the flash object sends the onClick event.
Its reproducible in sandbox:
<zk>
<flash src="http://www.zkoss.org/Steps/learn.swf"
height="300" width="800" onClick="alert('1');">
</flash>
</zk>
This is needable for drill down on flash widgets.
Bug fixed since 2011/07/13