i have three monitors on a Matrox TripleHead2Go. The Matrox TripleHead2Go simulate one monitor with a resolution 3840x1024. The Software Matrox Powerdesk control the programs to open in one of the tree monitor.
In a screenshot with greenshot the cursor is on a different screen than the selected range.
I use greenshot 1.1.8 build 35 (64 bit) with Windows 7 SP1 64 bit.
none of us have Matrox hardware, as far as I understood the software you use can only be used with Matrox hardware.
I will see if I can find something with Google, but it will be hard.
I experience the same issue on Nvidia. Note that I have three monitors, one has a different resolution. The one with a different resolution is my "main monitor."
This "bug" must be in the logic you are using, possibly expecting a square or rectangle, and when you end up with a, well... not that, your logic can't handle it, and pulls a single screen's resolution.
Worth noting, Snipping Tool does the same exact thing; but maybe this can be a(nother) reason I don't use Snipping Tool and use your software!