Rectangle selection rendering glitch with horizontal scrolling

[AngryCarrot789]

The text editor has a lot of text in it, such that the horizontal scroll bar is visible. When there is no horizontal scrolling, even if the scroll bar is present, then the rendering is fine (a regular rectangle).

But when I start a rectangle selection while the horizontal scroll bar is slightly to the right, I get this:

I can't tell if this is intended or if it's just a visual bug, because it doesn't look quite right...

And when you scroll further to the right, it looks even weirder: