Rigged mesh goes head over heels when MaskNodesHandsOff is used.

As the title says, I have a rigged mesh that I downloaded off the Internet.
When I try to manually control the Spine or the Pelvis bone by code, the shape goes head over heels in T3D 1.2. I use MaskNodesHandsOff, in code, to turn off animation on any of the above mentioned bones.

Any idea why this happens and how to fix this problem?

I searched all over the net, and I found out about 'Zeroing Out' bones in Milkshape. Not a good option, as I have to re-animate all the bones, and I'm not an artist.
I also know about how the turretShape (kind of) works, as well, I'm aware of all the resources and discussions available here on the resource and forum pages.

Thx.