The Quick Editor window can have multiple scroll bars.

On MacOS if you go to Settings > Appearance > Show scroll bars > Always and then open a QE window you will see there is an additional scrollbar around the window that moves a few pixels (you may need enough avatars to go off the bottom of the popup)

We should adjust the styles so the extra scroll area is not needed (the content is reduced by the few pixels), and cannot appear (by disabling overflow)