Import avatar mask does not have the same effect as manually created mask?

So I'm assuming that my usage or understanding is wrong but anyway:
Are import masks set in the animation tab supposed to replace "runtime"(asset) masks?

Basically for my test(using humanoid rig settings) I have a simple walk animation on the base layer and a shooting animation on an override layer.
If I use a non import mask(which masks out the legs) plugged into the animator controllers mask field, everything works as I would expect, the layers are blended with legs walking and upperbody in its shooting animation.
However if I set the same mask parameters to the import tab of the animation for the shooting animation, the base layer's walk animation is completely ignored(unless of course I plug the mask asset into the field). Is this the expected behaviour or did I set something up wrong? The manual states you can do either with setting it at import time being preferrable, but my usage would indicate double the work is required to maintain this properly unless Ive missed something major.

 

Hi,

that seem like a bug, could you please log it so we can investigate what is going on?
https://unity3d.com/unity/qa/bug-reporting

 

Alright, I've reported it as Case 1081194