There's a very annoying IE6 incompatibility in ZK.
<window title="I hate IE6" border="normal"> <popup id="popup"> <label value="Fail" /> </popup> <label value="Click me" popup="popup" /> </window>
When you click the label "Fail", you'll get a popup that is sized by its contents.... .... except in IE6 where the popup always has 100% width.
This can of course be fixed by specifying a fixed width for the popup, but this is typically ugly. If the application supports localization, you'll be forced to guess a good width for all localizations.