Nah. It just takes a lot of power to reboot. Though, that's still a large difference. I'd chalk half of that to innaccuracies and half to actual rebooting.
Yes iit's a large bug lol. I've seen as much as 30% difference after resetting and or turning the phone off and on. It's a big software glitch MF has refused to fix, maybe they can't, maybe it's a hardware issue with the 920. Whatever the cause it's the single biggest problem the 920 has had from day one.
Sad to say, there was once i charged my phone to 100%, reply a few whatsapp messages, the battery dropped to 20+%. So i rebooted my phone and it restored back to 96%.