Okay. This is really weird. I have applied blendshapes to my poly (the head surface) for facial expressions. And because of some stuffups (which involved the head not moving with the body when I moved the body control), I right-clicked on this surface inputs->all inputs and middlemouse dragged the blendshape node to the bottom of the hierarchy of inputs.
Now the head moves with the body.

HOWEVER, now when I apply a blendshape, it rotates the head slightly in the X-axis. When i apply another blendshapes it rotates more. So I don't know what the heck is going on! I didn't freeze transformations in any of the blendshapes.

Some advice pls!