Not sure about the theme reset. At first I thought, maybe, you slid the hold over while booting by accident and all your settings were reset. But you said that all of your other settigns were fine. (Unless of course all you other settings are set to default values.) So again, not sure about that one.
The remote play button is like the center of the cross. It's multifunctional so serves as select as well as play/pause. If you are in a menu to begin with, pressing play will select whatever is highlighted. Now, I'll admit, I'm speaking strictly off the top because my remote is down stairs in the car. So maybe someone else can chime in with something more technical.