Bug: Hours suddenly completely wrong

This a a rare and old one. Can't reproduce it but saw it happen occasionally. 

Don't know what it's triggering it, but sometimes retuning to watch from settings or so, I see the hours handle like 4 hours behind... Like 15h59 instead of 19h59.

Seconds hand is approaching 60... Since it happened before I already know that when the hour come it will resume to correct time, 20 hours in this case.

Anybody noticed this ?

The other times I saw it, I thought it was some crazy thing, but now I already saw it happen a few times over various firmwares.

I'm on latest firmware