So, basically the issue is that whenever an element is supposed to be wrapped inside a scrollbar, it's contents overflow the screen instead of being hidden (the expected behavior).

In the screenshot the list overflows downwards, but it also overflows upwards.

I have narrowed the issue down, and it turns out to be an issue with Optifine. I know Optifine is closed source which makes it extremely hard to pinpoint these issues, but I guess it must be somehow tampering with the way you render GUIs.

So feel free to mark this as a low priority issue, since the obvious workaround is simply to get rid of optifine.

I seem to have this problem as well, I also discovered that this could be caused by OpenGL not being able to load the stencil buffers.

That is correct. Something broke the OpenGL stencil buffers and BQ is no longer capable of cropping it's UIs. I cannot fix this from my side.