Snapdragon_77

Ok I did figure it out. In your screenshot I noticed the corner size option and I've never had to manually adjust that in any of the previous versions. Ty so much for helping me resolve this. Good Day to you.

I went back and tried it again. It worked fine as it did for you on a canvas size of 90x90 or larger. at 48x64 it wont work properly ill try to post picture.

I just installed the latest version of Paint.net, which I love by the way, and came across an issue. When I go to use the shapes tool, the rounded rectangle functions exactly like the ellipse. Not sure if its just me or if its a minor over site on your end but Ive never run into this issue in any of the previous versions. Just throwing out a heads up just in case others have experienced this as well. Again, Love the program and thank you.