It's a strange issue, two actually.
If I try to use the, let's call it the recolor function, to try to erase and recolor sprites of a certain color, it only does so on SOME of them, even though the pixels are identically shaded and colored, so I end up having to delete them one at a time.
Also, sometimes when I go to move a sprite, even if I have it set up so whatever color behind the sprite is set to be transparent, when I move it, the background is noticeably NOT transparent. Ranging from the entire background behind the sprite, to only a few pixels.
I've noticed this tends to happen with the pixels I've recently worked on, such as deleting the background behind a sprite, or something along those lines.
I'm currently using Windows 7 with the built in Paint.