I am still having the same problem on formpanel validation in mutiple tabs situation.
Each Tabs Item had it's own formpanel and when user click a button, the events basically
get each of the formpanel and called isValid().
As well, The tab panel is using getLayout().setDeferredRender(false).
It looks like the setDefferentRender does not work.
For testing purpose:
* I click button which trigger validation on both formpanel, it does not work.
* I click on other tab item and then click on button which trigger validation on both formpanel, the validation is working.