If the unit always locks in the same place, check the IR codes that you are sending and ensure that they are Clean. See the pronto/pronto NG FAQ for a discussion of clean codes.

You might also try backing off your Firmware to 3.7.7 or 3.8.11 and see if the problem goes away.

There is what has been reported to be a page jump slowdown (perceived memory leak) with the 3.8.14 firmware. A simple reset about once every 2 weeks may avoid your problem for now.

If all else fails...

You should email your PCF to ProntoTeam at Philips dot com. In the subject line, please indicate that this is a problematic PCF that causes a freeze from time to time.

If you have an exact set of steps/method to reproduce the problem, you will definitely help the engineers.