> leads to either remote side think that the call was answered
Maybe that's triggered by adding your own number? Since you're clearly on the call already, your own number is obviously going to answer immediately and that kicks the whole call into "active" (since you presumably want a call to become active when more than one person has answered) without considering that you've actually got A+A+B instead of A+B+C.
maybe - it's hard to tell, and I did bring up that other option as well. It's just that when a 1-1 call upgrades to a multiparty call, there should a be a lot of new stuff going on at signaling level to convert that 1-1 call to multiparty - and a chance is that it's a combination that leads to this bug - a call gets upgraded to a multiparty AND a number being added is already part of the call...
Maybe that's triggered by adding your own number? Since you're clearly on the call already, your own number is obviously going to answer immediately and that kicks the whole call into "active" (since you presumably want a call to become active when more than one person has answered) without considering that you've actually got A+A+B instead of A+B+C.