Anybody who can reproduce, please add a comment to the bug.

I now realise that my problem had nothing to do with the screen lock button and everything to do with random reboots when idle. I have looked at /proc/bootreason and sure enough, it has a value of '32wd_to'. Looking at file /var/lib/dsme/stats/lifeguard_restarts shows that once again,

...
/usr/sbin/dsp_dld -p --disable-restart -c /lib/dsp/dsp_dld_avs.conf : 2 *
...

I understand that dsp_dld is responsible for loading of the dsp chip, but fail to see what it could be doing when the NIT is idle.

I still think of my NIT as being in the 'integration' state; I have installed nothing that I'm not prepared to trash. It holds no data that I rely on. I officially 'don't trust it'. I can try out anything I like to see how it works and get to understand it. I'm prepared to re-flash it at any time. Hang it off the bed-post and stick pins in it. Anything.

My problem is that at the moment, I can never see it going 'Live'. If it is prepared to re-boot itself when doing absolutely nothing, how can I trust it to do anything reliably? I would love to just ignore the problem, but the re-boot ends up hammering the battery life by unlocking the screen. If there was any evidence of a hardware fault, I would bite the bullet and send it in for repairs. I'm getting close to regarding it as 'unfit for purpose', despite loving the functionality it provides.

Any suggestions on how I might proceed?