Why Does My Watch Switch My Zones "Based On"?

Hello,

I want to manually set my zones based on HR. 

I go into Menu > Settings > User Profile > Heart Rate > Zones > Based On. From there, I set it to "BPM". Then I go through and configure my zones. 

For whatever reason, I'll come back a day later or so, and "Based On" has switched back to %Max. Hr. 

Does anyone know why?

In Garmin Connect web version, I can adjust my heart rate zones under my user settings, but the available training methods are only %'s; i.e. % of Max. It doesn't give the BPM option. Is this why it's happening?

Anyone else have this experience?

Thanks.