Unity Avatar Mask refuses to see Master Bone as Root Bone

For some weird, twisted reason when I try to use an avatar mask to replace the animations on the hands, body and root of my character, Unity picks the hips as the root and not the Master bone, even though in the mesh renderer, the Master bone is selected as root.

I am trying to stabilize the movements of my hands when the character is running through a separate animation, using an animator layer, but when it comes to running, the hips are also moving, so the hands are also shaking like crazy. You would think that making the mask also overwrite body motions would solve this, but nope. So, I noticed that if I disabled the root movements in the mask, they fully stabilize, so that must be the solution. Too bad that when I do mask in the root, the character starts floating slightly...for absolutely no reason. I checked and both the hips and the root are not mid-air or something.

I am out of ideas. I don't know how to add the root to my mask to stop the hands from rotating without making him float. Any ideas?