Error When Trying to Add Motion Tween to a movie clip with parented layers.

Hi, i've been looking around forums and I'm not sure I found  this problem i've been having:

Basically I have a character that has body parts across layers which are parented. (Head > Neck, Upper Body > Hip, etc.). As soon as I rotate one of these parts, say the hip (with the torso) then try to apply a motion tween of 30 frames, it looks fine at frame 1 but at frame 2 and onward the parented object breaks apart or rotates somewhere else...

Here is an example of a parented leg @ frame 1 vs frame 2 without moving anything. If anyone knows what this problem is I would appreciate the help, thanks!