Hello and thank you for your replies!
Yes, it seems there is a focus problem when switching between ScratchPad and the normal area.
Anyway, I have good news because I found a much better way how to realize my wish.
Thanks to gregorbeyerle1, I gave the Arranger a new chance to see if it will be more suitable in this case.
When creating several Arranger sections inside of the ScratchPad, it's possible to access those without opening the ScratchPad.
By clicking on the Arranger tab (which is above the first track), you can see all Arranger sections.
When copying a section which belongs to the ScratchPad, you can easily paste it inside of the main area,
and there is no wrong pasting or creating of new tracks.
It gets pasted correctly at the cursors position.
Great... but there's still one issue:
When you left click on a section and press Ctrl+C to paste it, it doesn't work.
However, if you right-click on a section and click on copy, you can paste it.
Would be great if Ctrl+C would work here!
I attached screenshots to make it clearer.
Thanks!