Not sure if this is a bug or not.

Me and an AI were in an alliance.

the AI invited another AI into the alliance

in the diplomacy screen both the AI players are listed as being in an alliance with me.

the the last to join Is also in a "cold war" with me.

i let a few turns pass, but no change.

It seems like two alliances were made that had the same name and the same members.

later, there was a relation change where "alliance name" enter cold war with "same alliance name" ,which put me in cold war with all my alliance members.