Hi
This has actually been going on for several weeks or even months (certainly since 15.71b) and still with most up to date firmware.
My watch is set to 10pm-730AM power saving sleep mode. I occasionally toggle battery saving on manually if I don't think I'll be doing much on a particular day. I do not do anything odd or unusual with the watch otherwise.
I have actually managed to capture this today with a video!
(note some of the top right button presses are just finger trouble, not reproduction steps)