Was playing pvp, tried to make a build around Shinobu, turns out it either has a shadow nerf to the cooldown or is bugged. The exotic improves Skip Grenades and gives an additional charge.
Dying completely removes the second fully charged grenade in pvp or it completely resets the cooldown if the sconond charge isn't yet available. This makes it so you only ever have one grenade charge at a time and completely guts the purpose of the exotic. This is the only time I've seen a full grenade charge being taken away on death in any mode and I can't fund the chang in any of the patches.
-
Shinobu vow isn't the only armor that suffer from this problem, every armor that provide an extra charge(melee, grenade or class ability) will also lose the second charge.