Diana and Sated Devourer Passive Procs

I tried at Diana earlier with Sated Devourer looking to see if a build more suited to dueling was possible. It was somewhat infrequent, but it would sometimes proc the double passive stacks and sometimes would proc all three for Diana's passive.

Basically, sometimes it took 2 hits for Diana's passive AOE to proc and sometimes 3. I've seen this on some other champs as well, much more rarely, but still.

I believe it has something to do with the way the stacks count until they proc and the interaction with the Sated Devourer's Phantom Hit passive.