This has been documented before, it’s an issue with FitToWindow specifically. The emulator assumes you are using the actual resolution to detect scroll frame, you can verify this yourself if you switch to normal resolution and find the bounds for the scrolling are where the scrolling frame would appear there.
I am in the process of checking over bug reports and following up on some bugs that haven’t received any activity in a while.
Is this issue still occurring or can you confirm that this bug has been resolved?