The most simple button doesn't shows on mobile devices like iPad. It just fails when ZK detects that it's a mobile device, because it works with Windows Phone, that ZK doesn't knows that it's mobile.
I've tested <button label="Test" width="125px" /> and it don't works. Nothing is shown.
It seems like a degradation, because it worked on 22.214.171.124 and 6.5.2, but it don't works on 6.5.3, 6.5.4 and 6.5.5 .
May be it could be related with tabbox tabs not showing properly also on mobile devices.