The first thing I tried to do in Paint.net was to move a small (1 x 9 pixel) selection. But I can't, because every handle seems to be active within about 5 pixels of its position, so I can only resize!
I had anyway zoomed for a better view, but I find that the active area of the handle expands with the zoom. I'm afraid I can only regard that as a bug, since the handle icons do not expand and the activity of the handle should be directly related to the size of its icon.
This thread deals with another effect of the same problem.
In any case, how can I move a small selection?