Well two questions spring to mind... answer those and you have your answer...

1. How is my PIC handling MCLR? Internally or Externally?

2. If I have anything connected to the MCLR pin externally, am I likely to blow it up by applying a high programming voltage to it? Usually folks have +5v connected to MCLR, applying 13v or more risks having that high voltage being distributed around your board to components that normally are expecting 5v (and runs the risk that your programmer is now powering-up your whole board). In the words of Clint Eastwood as Dirty Harry... "Do you feel lucky?".