Email to MMS on iOS 6 shows two senders instead of one?

I've been using a group email to forward messages to several recipient's email and MMS. Ever since upgrading to iOS 6, the users with iPhones receiving the message through their carrier's mms email (1234567890@mms.att.net for example) show that the message was from two people, and not one. It shows as coming from myself, and then also the address that the original message was sent to (ie. the group email). The problem is, if they reply, the reply is sent to the entire group of 30 people instead of just me. Didn't have the problem before the update, but it is consistent ever since. Any idea how to overcome this? I've tested out iPhone 4, 4S and 5, with iOS 6 and 6.0.1.