Flush mount ceiling lights

[wecker1]

We have two semi-flushing mount ceiling lights in our bedroom slide. They operate off of independent switches attached to the lights themselves. One light remains on with the switch in either position, on/off. Driving DW crazy at night as well as myself. Two questions: 1) How do you remove the outer cover to the light?, and, 2) any ideas on the cause other than a loose connection? This only started happening recently.

I've tried turning and prying the outer cover off but only to the point where I thought further pressure would damage the plastic.

Thoughts please.

Thanks in advance!