Asterisk mail greeting change when using different codecs

Hi guys;

I’m using X-Lite as endpoint.
When i use the VoiceMailMain() app i get different greetings depending on decodec i’m using.

For example, if i use codec G711 A/B the greeting says … “Welcome to Asterisk mail” … if i use GSM it says “Welcome to Comedian mail”

Is this a normal behavior?
Why is this happening/

I’m just curious.