I have to disagree here.
The power save mode is not on as default and doesnt kick in.
Unless you set power save to turn on and therefore get the notification in the top the phone should not go into any power save settings.
My phone didnt do any of this until I 1st turned on Power Save and then tried to turn it off.
I have done a reset on the phone using my HTC Account back up and it took no time at all.
This issue no longer exists. And for some reason the battery life has improved as well.