When attempting to register a jabber account (through the gabble backend, in this case) the connection attempt fails with "name in use" - the only way to get around
this appears to be to delete the account from the list and add it back with the "Reuse existing account" radio item selected (instead of create new account).

This is potentially confusing for the user - I think we should either inform the user that the JID exists and offer them the opportunity to connect to it or remove the "create account" flag and try to connect automatically - I have a slight preference for the first choice as the user may care that the account 
already exists (eg if they realise they are connecting to the wrong server 
and don't wish to submit auth details).

From discussion on #telepathy: Depending on the approach taken, it may be better to fix this in telepathy rather than empathy.