Scrolling up scrambles lines together.

So I have this problem that only happens in full screen mode.

Whenever I scroll up to read something, the lines get all scrambled together, making them almost impossible to read. The picture should help clarify what I mean

This always happens. If I select text, it reverts back to normal, so I’ve been « ctrl+a » all the time, but it’s annoying.
I’ve tried to turn off typewriter scrolling but it doesn’t help.
Any ideas? I’m on Windows.