Take your pick...

Bad code, or
Bad PIC, or
Bad Circuit.

Since all pins operate pretty much independently, you either have a short between it and an adjacent pin somewhere, or you have a dud PIC, or your code is flawed (which includes not initialising the PIC properly or resetting the PIC in some way into it's initial power-up state). Are you perhaps using some command which is not valid for the 12 series PICs?