This is an intentional change upstream, the connection now automatically 
happens in a new tab.

Ew, yes, I'd come to that unfortunate conclusion. Fixing summary accordingly.

Uh, I may be missing something, but why would you want to replace the server 
you're currently connected to with another and why doesn't simply closing the 
tab for the "old" server do the job in such a case?

Channel tabs have history. That history is lost if you close them and open a new
one. (Admittedly, it's also lost or at least completely mangled if the
three-year-old bug #123335 kicks in when you reconnect, but at least that
doesn't happen _every_ time.)

The 'new' server also ends up on the right-hand-side, in a different place to
where the original channel tabs for that server were. I haven't worked out how
to move it -- I can move channel tabs _within_ the block belonging to each
server, but I can't move the whole group of tabs belonging to one server, en
masse, into a different position w.r.t. other servers.

Look, there's no way we're going to implement this feature in Fedora, even if 
some form of it used to be in old versions.

I CCed upstream on this one. Zed, what should we do with this one? File a RFE 
at your upstream bug tracker and then close this one as UPSTREAM? Just close it 
as NOTABUG?

*shrug* There's no room in the network-list window to put in such a button and
it looks ugly anyway. Just trying to design a "good" UI, the pain of progress.

If you click Connect and you're already connected, it'll open a new tab(s). If
you're not connected, it'll reconnect in the already open ones. Isn't this good
enough?

I'm pretty happy with the way it is, who really wants a 3rd button in that window?

I personally also think the current UI is fine.