not having personal experience with that problem worst case the radio is knackered , but you may find that your radio is loosing power when u switch off the key what i'm saying is there may be 2 power leads to ur radio one stays live permenant and one goes dead when you take out the key- check all fuses before anything else .
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.