Today we discovered that in FM12 an empty overlay tab panel blocks tooltips from triggering on underlying display fields — as well as blocks us from using all the new button/field mouseover effects.
We rely heavily on overlay panels for special entry and to display user help. They are used on over half of our layouts and greatly enhance the user experience. We see no reason FMI couldn't have provided the same "see through" effect that has existed since FM8. It is obviously an oversight, but this one is a showstopper for us. Until it's fixed, we're stuck with FM11.
Any overlay panel that is empty should be disregarded by the tooltip and hover processing.
Or, if FMI wants a specific indicator, the Object Visibility attribute (Sliding and Visibility) can be used.