Usb mtp / msc???
Are you charging using the regular charger or a usb cable connected to a computer?
the USB connection is most probably MSC, i.e. as a mass storage device. which is why the ringtones are reverting to the default ones since when usb is connected, the sd card no longer be read by the phone.
change usb mode to MTP, and see the difference! ooh, and check if smart connect has any events set for the charger connect / disconnect events as well...