Cody Fink with one of the most frustrating complaints on iMessage, one which I share:
If one person in the group was sending from a different address, it would cause a new conversation to appear in iMessage (thus “splitting the thread”) for the receivers. For the sender, everything would appear to be the same. With a big group of people this became a daily annoyance because it became difficult to follow conversations when different instances or pieces of it showed up in different places. It’s a hard problem to describe, especially when receivers can opt to receive messages at multiple email addresses (and if the same person you’re conversing with decides to send you something to an alternative address, I believe the message should show up in the same conversation). The reality is that the settings are kind of a mess and talking about this stuff caused a lot of frustration and we eventually gave up.
The worst part is I feel like iMessage can do these things properly and I’m just not smart enough to figure out how. The account settings and how they tie into your contacts are seriously convoluted and really, there’s no reason for them to be.