Thanks for the reply. This is probably it.
I probably have put a DIV around the question. Because I also have a line separating the questions and when questions are hidden due to conditions, this line still shows (this is a "bug" in my template that I was aware of, but never really went to fix it). It is probably time and this here is additional motivation, because this workaround here can be pretty useful.
But I wanted to use a different base for my template anyway, like the Skeletonquest theme from Dennis or the one from the Dutch guys. But I just didn't have time to look into this yet.
You can spend loads of time with creating templates...