Constraint Blend Physic Anim Problem

Hello all! I have a skeletal mesh of my character and a static mesh of a hair. I have a constraint, that attaches hair to mesh(everything on lock). I get transform of a socket placed in head(which is exactly the same as transform of a head bone), then I’m setting transform of hair to that mesh and constraint this together(mesh and hair). Problem is, that I’m using a BlendPhysicAnim, and during this blend, hair goes crazy. They looks perfectly fine everywhere, but not during this blend. Do You have any sugestions? Ideas why this is happening?