Bizarre SMS glitch - merging unrelated messages

[Schmactor]

Both my wife and I have been experiencing this problem at the same time. Our accounts are not linked in any way. Text message threads are being merged for no reason. Let me explain. I will call myself A, my wife B, and our friends C and D. We had a group text message thread going with A,B, and C. Then D sent a group message to A and B (nothing to do with C). However, D's message appeared in the first thread with A, B, and C for no reason. And we each got a different notification on our messages. A's said that D added D to the conversation (which should be impossible). B's said that a phone number added D to the conversation. And D's said that A added C to the conversation. This is very bizarre and also a privacy risk since random people's messages are being added to entirely separate threads. This kind of thing has happened a few times. What could be going on?