Alpha-numeric keypad during call

Hiya folks

Apologies if this has been posted elsewhere ( I did search to no avail ) or is a completley stupid question but am hoping someone can help....

When making a call the alpha-numeric keypad is displayed as usual, but as soon as the call connects, the letters disappear......Wasn't a problem I'd noticed in the month or so I've had the Galaxy, until calling my service provider tonight and being asked by the recorded voice to input letters from my password.......Is there anyway to get the letters back? Is it something Samsung forgot, or a fault? I've seen a similar thread on the Android forums with no joy there