I have seen this problem with my recently acquired HDR2000T. The first time it happened, I was advised by Humax support to perform a factory reset, which seemed to fix the problem, though the second time it happened, putting the box in standby and restarting it achieved the same result (as you have found). I have not seen the problem again (in a couple of weeks of operation) but it definitely exists. That’s not much help to you, other than to confirm that the bug is definitely there.
I have my HDR 1800 set to turn off at 2am and back on again at 5pm.
A couple of times after it has auto started I found that the Media button did not do anything.
Turning the device on and off a few times seemed to restore the functionality to the media button.
However this evening I had to power off at the wall before the media button worked.
Any clues to what is going on?
I had that very same issue with our 2000T. On a hunch I disabled the time on time off I had set up. The issue disappeared from that day forward and has never resurfaced since.