@jimbop
It may surprise everyone, but not me at all, that I didn't get a reply after some 10 days or more.
Now as usual one is always best helped by yourself.
So I found the solution myself, but came back here to help those that had the same issue and couldn't help me either.
The solution can be found by reducing the zoom level below 125%. Mine was set at that level and by reducing it to 110% (temporarily) I could access all the buttons of the GXControl.
Issue solved hereby.