Annotation Shortcuts inconsistently working (3.6.16779 64b W10)

[meteorquake]

Just now - and it's the second time it's happened - all my annotation colouring shortcuts disappear and only 'A' -> Yellow is available. I dare say this might be a general issue with all the shortcuts, but I'll describe what I experienced.
I close Sumatra and open it, and the problem persists. I open advanced settings and all the shortcuts are there; I copy and paste and save there to try to get it to recognise it, but no luck. After closing again, at some point a few minutes later when I open - the same files - it's all fine with the shortcuts suddenly working.
Not something that's currently reproducible but perhaps it might be possible to think of what's causing it given this is not the first time.
Cheers, David