Thanks @mrcdk, you are right. Disabling the Control.clip_contents solves the problem.
I will probably be using the scrolling, so I’ll look for an alternative.
Putting a text line above the table solves the problem with the top border.
I tried putting empty columns on the left and right sides of the table. This fixes the border on the left side but not the right. If I find a way to do it, I’ll post it here.