HDMI Resolution Changed by Itself

I set the HDMI resolution to 1080p 60Hz with auto color space. It would play fine. But a couple of days later, I sometimes find that it has been changed to 720p. How do I prevent it from changing the resolution by itself?

This kept happenning to me all the time after powering off the WDTV (i.e. 3-second shut down, or disconnecting the AC adapter). In the end, I set the resolution to “Auto”. Now every time the WDTV powers on, it starts at 720p, but while booting it changes to 1080p, which is what I need anyway.