How to make masks work for Legacy animations?

When I use the legacy animations (because the other versions don't import the animation correctly), the masks don't seem to do anything.

I have a blend file with 2 rigged characters and a vehicle in it, I set the type to legacy as otherwise the animation isn't correct, but I want the ponytail of 1 of the characters to be procedurally animated, so I need the ponytail-bones to be masked out so they don't have keyframes. (as the keyframes overwrite the procedural animations).

I this a know bug, or is there a way to do this?