I recently received a bug report on OnTopReplica, because it did render incorrectly when in High DPI mode. Some UI elements did slip beyond the window boundaries or were misaligned.
Even if Windows Forms simplifies high DPI mode the problem (Control instances have a special AutoScaleMode property that automatically adapts your UI based on the system font size or the DPI mode), you still must be certain to never ever use constant pixel values in your code.
Essentially, the code that handled the opening and closing of the "region" side box did increase (or decrease) the width of the form of a constant value (which I tought would always match the size of the region box control). Unfortunately, Windows Forms would automatically adapt the size of said control, thus making it bigger than expected. The solution is quite easy: simply drop every constant value and always refer to the actual size of each control (in Control.Size and Control.ClientSize).

The new version can be downloaded now via ClickOnce. As seen in the screenshot above, OnTopReplica 2.6 now also includes a "chrome less" mode that will remove the classic window borders (and make the application unresizable, even if it can still be moved). Should be much nicer for videos and similar.
Unfortunately, while publishing the new version I discovered that the original license I used to sign the ClickOnce manifest had expired last month (this means OnTopReplica was first published with ClickOnce around one year ago, woot!
). I had to sign it with a new key: should you encounter manifest or license problems when updating the application, please update .NET to version 3.5 SP1, which should fix all manifest problems.