[Freeswitch-users] capturing alphabet characters from session:read()

Hello, I have a Lua IVR app running on Sangoma PRI/FreeTDM. I am getting some funny dtmf input from time to time where session:read() returns an alphabet character (usually "A" when it does happen, less frequently it returns "D") instead of a digit. I am not able to reliably reproduce it, but posting the question here in case anyone can point me in a direction to troubleshoot this. Thanks in advance, Neil