Router restoring default passwords after power turned off?

I recently changed the passwords for the 2.4 and 5 channels, my networked devices have all been set w/ the new network password succesfully, but when the network was powered up this morning nobody could connect wirelessly. A check of the router showed the passwords were changed back to the defaults - I know the reset button will restore the defaults but I've never had this happen with simply turning off the power to the router.