I'm not much help, because I never do animation in Vue, but I just wanted to say I understand your problem (I animate in Max).

I did a quick check, and got the same results as you. And I couldn't find a way to stop it.

But I did notice that it only added ease in/out to the first and last keys. Any key added to the middle of the timeline was smoothly passed through. Maybe you could make the first and last keys out of the range of your rendered anim?