Sounds like a firmware glitch to me. Try to get a firmware upgrade (usually from your service provider's authorized service centre or a local cellphone place that knows what they're doing).

If it's been used for a while, try doing a master reset, not memory reset..master reset will not delete your phone book in most cases, some do, please check your phone manual before you do a master reset and shut your phone off and turn it back on after 5 minutes, usually clears the temp memory on the phone that its been pilling up.

Cy