Hi,
When using the tool shapes (ellipse, star, diamond, trapezoid used as example) coupled with very small sizes down in the 10 or 20 pixel range, as well as having AA for the tool turned off, Paint.NET produces some very wonky and irregular shapes.
Now AA off should result in some of what we're seeing, but it should also result in symmetry, using proper mouse locations without that 1-pixel overshoot etc. Try creating a 20x20 canvas, selecting ANY of the shapes with AA off and then drawing that shape out from 1x1 to 20x20, see how the shape progresses. IMO this could be improved.
Using PDN 4.2 beta as of Jul 2nd.
See: