I use 2560x1440 for everything, it's the native resolution of my 32" monitor.
When I decrease the display resolution, the problem is exasperated.
The menu drop downs used to be fine, but it's been a year or so since I've done this type of work, and
I can't do anything productive until I get this sorted.
I tried uninstalling Paint.net, I deleted all the Windows registry items relating to PDN, re-installed after a reboot,
and the problem persists.