Darius Ult

In the last game I played I noticed something weird; I understand that at rank 3 Darius' ult is supposed to reset completely on kills which is completely rad. However, I noticed something weird. I ulted at the same time an Akali ulted in and she got the kill just after my animation was finishing and it looked like damage was dealt too but the ult was still reset afterwards. I'm not certain if there's some other factor I didn't take into account but it looked like I got a reset off of that assist rather than it being reset from a successful kill.