Just upgraded from 520 to 540 a few months ago. When the 540 is powered OFF and I plug it in to charge, it will turn itself ON. I manually shut this off while plugged in. When I return to the 540 (still plugged in) it's back on. I shut it off again. return a few hours later and notice that screen has "GARMIN" like a boot up screen, but it's not moving to the ON state, just stuck there. From here I initiate another OFF cycle, but the unit turns ON. so back to the power button for the OFF cycle. I check the battery level first, if at 100% i just unplug and make sure the unit of OFF. From here it stays off if unplugged. As soon as I plug it back in, it's on again.
This is also true for my EXPLORE 2 units.
All of this ON cycling is triggering my VARIA to turn on also...additional headache I don't need.
Come on Garmin. PLEASE remove these rather useless power ON triggers in the firmware. We are all smart enough to turn our bike computers on when we want to and off when we want to. Anything else is a PITA.