I love paint.net, used it for years and was really glad to see there's finally an update.
However, I'm surprised to see the only major bug that bothers me hasn't been fixed.. I can't be the only one that notices it.
To replicate the issue, create a new image with dimensions 1px by 500px,
Fill it in with a colour,
Zoom in to 2550% (occurs at some other random zoom levels too)
Scroll to the bottom of the image,
With the select tool, try and select the bottom of the image.. - it selects random chunks.
The way I get around it in day to day life is to stretch the image much wider.. do my work, and then shrink it back down again to 1px
(which is a big pain).
This bug doesn't just occur when it's 1px, it can be 5 or 10 sometimes too.