Would definitively happen if you or the person who owned the S1 before you did pen modding.
I didn't know what this was so some googling and took a look at the board and the resistors R3, R66, R38, R52 were all colored black.
I just took an eraser to one blade and that seemed to do the trick!
http://imgur.com/bc6BsjfThank you for the speedy reply!!
Edit: I'm going to check the other blade and see if that's the issue with that one as well! Will post more results!