I just KNOW that I'm going to kick myself in the pants when I get an answer to this, but; Windows XP, Paint.net v3.5.5. I use the selection tool, select an area, and copy the selection and then paste. Unfortunately, it also selects the background as well when I paste. I don't know how I've done it before but I've been able to paste things that I've copied without the background also being copied.
NOTE: Yes, I'm aware of the Magic Wand for basic images. I'm not referring to it's usage, however. And I've also only had this issue within the past month or so, as well- I never had a problem before. Possibly an update, or more than likely a change in something I've been doing I just don't recall doing now. Please keep things relatively simple, since I usually just use the program for minor picture editting and resizing. x_x;