The slowness in that bug may simply be some kind of timeout being hit due to a dbus connection problem. After the timeout, maybe it retries and succeeds, or tries some other method.
I also have unsubstantiated hunches that:
Bug #976638 (pkexec does not find any authentication agent)
and Bug #1193236 (Couldn't connect to accessibility bus: Failed to connect to socket /tmp/dbus-*)
The slowness in that bug may simply be some kind of timeout being hit due to a dbus connection problem. After the timeout, maybe it retries and succeeds, or tries some other method.
I also have unsubstantiated hunches that:
Bug #976638 (pkexec does not find any authentication agent)
and
Bug #1193236 (Couldn't connect to accessibility bus: Failed to connect to socket /tmp/dbus-*)
are also affected by this.