I noticed, while using VNC that a small offset is noticable while doing mouse interactions.
The easiest way to reproduce this, is to go the desktop of your OS and do a right mouse button click. Usually, a context-menu pops up. However, it is offseted by 10px from the top and 10px from the left.

After investigation, the rounder border box seems to be the culprit. Disabling this solves the offset issue (and IMHO looks a bit more modern even)