You can add Log(100%y) and see whether it is correct or not.
Added to Activity_Create.
First time I launched "the app" it resulted 671. Closed (back) it is 696. So the difference is 25dip, which is often a standard measure of some stuff, like title bar or other bars.
Third time, again 671 (and then the button is in the right place - or I should say it is fully visible)
Before this I have also updated the firmware.
I might reset to factory settings.
There are other strange cases, with this tablet; at times, leaving some app, the "home page" is defective... horizontally, though.