Quasselcore's (SSL) connection code is not error-tolerant (git-611ebcc)
When Quasselcore connects to an IRC network and the connection fails, no notification is given to the user and the core's state becomes internally inconsistent. The core will report the network as connected even though the connection failed. (Note: This is attempting SSL-secured connections. I have not attempted to reproduce this with non-SSL connections.)
As an example I was attempting to connect to a server and the connection hung, so after hitting "Disconnect" a few times I deleted that server from the server list (currently the only way to make Quassel try a different server) and tried a second server. When this also failed I deleted all the servers from the list and substituted a third, however clicking Connect still attempts to connect to the second. There appears to be no way to correct the situation other than restarting the core - if there is a connection in progress, there is no way to stop it since the core believes it is disconnected and offers only a "Connect" option.