i can confirm that this happens, i was going to make this thread this morning but osk beat me to it
the autoreconnect doesn't repeat all the status messages ever seen, just the ones in the backlog (sent again during reconnection), so i suspect that the message deduplicator does not recognize the join messages and they are repeated
there is one another bug with reconnections and users leaving, but i need to document it first and then i will make a thread (i hope i won't forget now once i've written this down here)