Default weird thing just happened

I put my phone on silent last night (I do this every night) and also on ultra power saving mode. I don't like to charge my phone overnight so I put it in UPSM to last through the night without it dying so I could still get my alarm to go off then charge it this morning. I also have my phone password (not PIN) protected (I have curious kids lol). Anyway this morning I charged my phone and turned my ringer/sound back on. Then I restarted my phone (I like to do this too btw) and my sound/ringer turned back off when it came back on after the restart. I had to turn it back on even though I did that before I restarted my phone. Any ideas? This is the first time its done that. I don't know if its because of the UPSM or what. TIA