When dialing from the Mesh Potato the channel driver generates call progress tones so the person dialing can determine the progress of the call. For example first their is dial tone, then when the number is dialed you here "ring back" tone indicating that the other end of the call (the B party) is ringing.
The problem is that ring back tone is heard even if the IP dialed does not exist, i.e. the MP hasn't actually connected with the B party SIP device but ring back is still played. It would be better for silence to be heard until an actual connection is made with the B party. After a time out if there is no connection a busy tone should be played.
Fixing this bug is probably a matter of processing the Asterisk events passed to the channel driver correctly, i.e. don't start playing ring back until an event indicating a connection to the B party is passed to the channel driver.