I have noticed in few QSO's with low signal levels or other issues with a lot of retries that the transmit buffer (Messages currently being sent) is not flushed after the other party has sent <DISC> successfully and the QSO has been finished.
In these cases my transmit buffer had included my '73s' canned message including the <DISC> command. With the next QSO, being either the calling or called party. this remaining buffer has then been the first thing to be sent in the new QSO, eventually disconnecting it immediately.
The only way to get around this now is to close VarAC and restart.
I recall seeing a feature request of possibility of clearing the transmit buffer but could not find it now so I don't know the status of that or is it related to this finding.
Erik OH2LAK TF3EY