Annie's cooldown begins when Tibbers is summoned; Yorick's cooldown begins when the Maiden dies. Yorick has no cooldown to reduce for kills he gets while the Maiden is active, but Annie does. Thus, Yorick's interaction isn't bugged.
Also, I'm fairly certain:
- Yorick is the only champion with an infinite duration on an ability - and so is a terrible counter-argument, since he would probably be a candidate for an exception anyway.
- Presence of Mind is 10% of current cooldown, not 10% of maximum cooldown, so even if Yorick got 50 kills while she was alive - she still wouldn't be immediately available to cast the moment she died.
Although even if it was possible to get 100% cooldown, I'm not entirely sure why that's unfair or something only two-cast champions can do.
- TF uses Gate and gets a pentakill - his cooldown is reduced by 50%. Enemy team respawns and rushes to defend, he gets a second pentakill. Gate is now back up.
- Annie uses Tibbers and gets a pentakill - her cooldown is reduced by 0%, because Tibbers is alive.