Here's a screencap of it:
The thing is this only seems to happen with images I've copy/pasted into PS. If I open a picture saved to my hard drive, it comes out normal when cropped. If I create a new file and paste the picture in or use "new image from clipboard," the crop comes out with this border.
This just started happening yesterday, so I'm not sure if I hit something by accident or something's gone screwy or what. Any help would be greatly appreciated.