Please, Klaus, see the image well... I set Show Title = False and Full Screen = True.
I'm thinking that the problem is also related to the Grid setting.
After many tests, setting it to 10 then to 50, closing and opening the Project again (not just the Designer) the button sometimes will be completly out of Designer or half inside it. Randomly
[correction: a label I added will be outside the Designer, not the button; but the error is there, anyway]