About those "deponent" verbs...

When -(θ)η- was first integrated into the aorist, it involved not just a change or affectedness for the subject, but a complete change of state. If we look back at the two predicate types involved, this includes the telic-transformative lexemes as well as the state predicates. It is this relationship between change-of-state/telicity with the perfective aspect of the aorist that defines the -(θ)η- in contrast with the other middle inflectional forms. The aorist perfective aspect aids in this process because it expresses the fulfillment of that change, so that the new state is fully reached or totally complete. If a middle form is used in the present stem (imperfective), it indicates that the subject is undergoing change but it does so as a progressive reaching of the state so that the change is not fully reached. This is a difference between ἐτήκετο “it was melting” in the imperfect and ἐτάκη “it melted” in the aorist. When used with the -(θ)η- aorist stem, the change is fully complete.—Rachel Aubrey in The Greek Verb Revisited