This is Paint.NET 4.0-wide Bug for me:
When clicking very fast with some Tools (Example: Brush or Eraser) i get a pixelated Image next to the Mouse.
Picture:
A Video (Yes, it was made knowingly in front of the screen):
http://youtu.be/6bgJZlvTDgQ
My System:
https://www.sysprofile.de/id162155