this may happen in a few contexts, such as connection exhaustion, but more importantly, when a request is retried in a different connection; if the request successfully sets the callbacks before the connection raises an issue and the request is retried in a new one, the callback from the faulty connection are carried with it, and triggered at a time when the connection is back in the connection pool, or worse, used in a different thread
this fix relies on :idle transition callback, which is called before request is routed around
88f8f5d287