What device?

Is it caused by the on-screen lock button or hardware lock button?

The hardware lock button is handled by MCE and adv-sys only detects the signals so screen should always lock or unlock. The on-screen button, in charging mode, always tells MCE to lock the screen.

I can lock the screen with a on-screen or hardware button and then use any of the other hardware buttons to control the device but the touchscreen remains locked. The hardware lock button always unlocks it. So it sounds like you either have a problem with your hardware lock button or MCE.