With power switch off and battery fully charged, I pull out my SD card to extract some pictures. When I'm done, I put the SD card back into my 60D and close the card cover. A day later, when I want to take photos, I discover that my battery is dead (the power switch was off the whole time). Once I pop in a fresh battery (I have 2 batteries), everything works fine.
If I put in my SD card after extracting photos, then eject my battery and put it back in while the power is off, I don't get this issue. This tells me that perhaps when I put in an SD card (even when the power is switched off), ML is trying to do something buggy.