All
I've seen this for a while now (old Yosemite betas and potentially before) where if you join a Jabber group chat room in iMessage that any message I post has 2 issues:
1) The message appears at the bottom of the chat and out of sequence when others reply. i.e. I say Hello, someone else says Hello but their reply appears above mine instead of below even when they sent theirs later. Therefore iMessage is displaying them out of time sequence
2) My messages are double or triple posted in the chat room.
This only ever happens in group chats through Jabber and not when I am direct IM'ing someone even if still using Jabber as the medium.
I raised a bug on this a while back and it was closed as a duplicate to another bug, one that is still open.
Wondering if anyone else see's this behavior and has any suggestions as have not seen this behavior change in El Cap beta 1 or 2
Thanks