Whenever I turn off the player with the battery switched on and an ac adapter plugged in, the next start, player formats everything and asks for new firmware. I also found that I can't, for the life of me, use sendfirm to install the bootloader if the battery is switched on.
I bought used so it might be an HDD issue, but it's strange that the issue only comes up under specific circumstances. I'll replace it, and reply.