I have two channels, one regular open #a and one restricted #b with modes +if #a. I am in both channels with two irssi 1.4.5 clients. #b also had an +I $a:JAA originally. During a network outage, #b ran empty. When the first of my clients reconnected, the channel was recreated, and the ircd restored most modes but notably not the +I (as is usual for list modes). When the second client reconnected shortly after, it was therefore unable to join #b. In the status window, JAA #b is already on channel (ERR_USERONCHANNEL, numeric 443) appeared. So far, this is reasonable enough.

When I saw that this had happened, I restored the +I mode from the first client. I then tried to rejoin the channel from the second client, but /join had no effect, i.e. no JOIN was sent. After a /part, which resulted in an expected #b You're not on that channel error (ERR_NOTONCHANNEL, numeric 442) in the channel window, I was able to /join again. (I did not test /quote JOIN #b.)

It appears to me that irssi still thought I was already in the channel despite the fact that the server had never sent a corresponding JOIN #b in response to irssi's JOIN. I'm not seeing any ERR_USERONCHANNEL handling, so that's probably not involved.