Hi Bernd
This is intended behaviour. I had thought about that option, but decided against it - I am always trying to maximise the space for the lyrics, so they can be scaled as large as possible. The page buttons do overlay on top of the lyrics, but they can be set with lower opacity to allow the text behind to still be visible. I have also added (for beta 11) a toggle to use smaller page buttons.
Hopefully you understand the reasoning behind this. Most of my users run the app of a screen size smaller than 7 inches. If I placed the lyrics inside the margin created by the page buttons, this would drastically reduce the lyrics/chord font size.
Gareth