Can't Move/Copy Selection

onelegflamingo

When I use the selection tool, I create a box around what I want to move/copy, but using ctrl + drag or ctrl + alt + drag, copy paste, just dragging... nothing I do makes a difference. The outline of the box moves or is copied somewhere else, but the image/color from inside the box is not moved or copied. The box is blank inside. I thought it might be a problem with the layers, but I don't have multiple layers. There is also a bar at the top that says "commit" or "cancel," but neither of these buttons do anything when I click them (nor does the bar ever disappear.) I'm not sure what I'm doing wrong. Any advice would be appreciated. 

onelegflamingo

Further Details: I am using a tileset that someone else made, and adding and modifying the tiles. I can copy/move other parts of the tileset. The first building I recolored works fine with the selection tool. The second building however, won't work at all. When I ctrl + drag, the selection area becomes blank/empty, but the original image does not actually move or if it does move, the original image inside the selection is not visible in the new location. There is something about these particular tiles that is causing problems but I don't know what.