Signature issues with shared inboxes

Hey folks, Weird issue here, we've now had 3 different accounts that have shared inboxes have local signatures replaced with another signature. The first one I am pretty sure it was because someone changed their From: and it replaced the signatures with that one, but now I've had it happen on 2 different accounts and it's just weird it's all happening at once. I'm going to keep digging, but I wanted to see if anyone else has an issue similar.