If I expand any data in the net menu I can't see any of them unless the string is really long. But even then the first part of it is cut off. It seams like there is a big rectangle hiding the text but i really don't know how to remove it.

If you enable the key fix in /nbteditor config, does it fix this?

I just figured out the issue:
While working the latest update, I realized that the MultiLineTextFieldWidget didn't check the key fix.
I have already updated it in the development code, and the change should be out in the next update.
I had just forgotten about it :/

For other people's reference: #6

I have this already enabled, because I work with a Mac. By the way the key fix isn’t the problem either, because if I disable it and click an the invisible buttons I have the same issue.

I read #6 before, because I had the same problem. Thank you very much.

I've just released v1.9.0, which fixes this problem. (I don't have a Mac, so I can't guarantee that.)
The update also renames the config option to "Mac Border Patch," and makes it automatically enabled for new Mac users.