This is what happens when I try to fill the selection with black.
It's super janky! What I want is to turn off all feathering to have a perfect crisp edge, but I can't figure out how to do that. Sorry for German interface, I would set it to English if I could. The option bar at the top for the selection tool says "Weiche Kante: 0px", which means feathering I think. "Glätten" means "anti-aliasing" and it's grayed out.
The paint bucket tool also doesn't seem to have any helpful options.
I'm using CS6 btw.
Edit: I think I know what's going on. The selection is essentially an alpha mask and isn't binary. The outline is just trying to give me an idea what the mask really looks like. It would be nice if there were just a button to make the selection binary without jumping through hoops.