For what it's worth... I have a radio (a Yaseu VX-1R) that has similar symptoms. When the battery gets very weak the radio loses all of it's setup information. After the battery is replaced I have to go through an extensive manual reprogramming procedure to get it working again. (I stick to Kenwoods or Icoms now.)
The symptoms reported by the OP sound more like
the device forgot it was a Radio in the first place ;D
Is anything connected to the pins 0 and 1?
If not you could permanently pull them high with a 10K resistor.