Similar things have happened to me with Benediction (the spell going on CD, myself or my target still dying), and strangely, normal healing spells. For example, I was trying to heal a fellow FC member of mine on a recent Titan kill who'd gotten in a bad way. They were at pretty low HP. Their combat log registered my heal for 900-something first, but a second later they took a couple hundred damage (significantly less than what I'd healed for, but more than their original HP pre-heal) and died. So the game effectively ignored my heal, even though it went out, we both saw the amount registered on our screen, and the damage happened after.