>        if (old_owner[0] == ':')
>        {
>            /* it's a unique name - maybe it was handling some channels? */
>            _mcd_handler_map_set_handler_crashed (priv->handler_map,
>                                                  old_owner);
>        }

Both occurrences of "old_owner" here should be "name".

Consider a handler with multiple names, like the fake Kopete in test/twisted/dispatcher/bypass-approval.py:

* unique name, say :1.94
* main well-known name ...Client.Kopete
* sub-handler to claim special channels without approval, ...Client.Kopete.BypassApproval

Now consider what happens if Kopete no longer wishes to bypass approval. MC sees this NameOwnerChanged signal:

* owner of ...Client.Kopete.BypassApproval changed from :1.94 to nothing

That shouldn't cause it to take any special action (except removing the .BypassApproval filter). However, because of the above logic error it's interpreting it as if it was:

* owner of :1.94 changed from :1.94 to nothing

which is what happens if Kopete crashes, causing all its channels to be closed.