BB Pearl :: Some Key Presses Result In Double Letters?

Pearl 9100 - some keys, particularly the top row return a double character even if lightly pressed once. For example, if I press the E1R key, it sometimes returns e and r (even if I am really careful). The space bar sometimes also results in a period even though I've been careful not to double press.

This is a new problem not experienced before. It is particularly frustrating when trying to input the password to unlock the screen because the attempt often results in an error.

I have re-booted the device (battery out) and it seems to fix the problem for a moment, but the problem quickly returns.

I have also set the Key Rate to 'Medium Fast' and 'Slow', but with no apparent improvement.

Firmware package Package Version: 5.0.0.1083 is installed (current for Telstra) and there are only a few third party apps (Google Maps v 4.52); Virgin Blue Travel Application; Telstra's My Place; and Sensis Whereis Navigator.