I did some quick googling, and here is a quote from one of the sites :
EEPROM corruption from brownouts
Brownouts can cause the first location of the on-board EEPROM to be overwritten.
In addition to the precautions elsewhere on this Wiki, consider not using the first EEPROM location.
Brownout fuses
If the voltage on your chip goes too low it can start executing random instructions, or corrupt the flash/eeprom (see above) so just always set the BOD unless there’s some good reason not to!
Food for thought, it may be worth using the BOD, and see if that helps, I know I haven't enabled it on my boards...
Russell.