When ibis_client_stop is called, it will set IbisClient:connect to FALSE and IbisClient:error to the input error.
The IRCv3 protocol's notify handler for the first one disconnects the account, so the notify handler for the latter should not also disconnect the account. It is sufficient to just set the account error.

Connected to a IRC that kicked me, and didn't see any warning about purple_account_disconnect being called when already disconnected.