Animation Problem

I am trying to make an animation of myself head opening the mouth,I have three objects the first is my head the other is the gum with teeth and the armature,i have parented the gum with the teeth with the armature and i have weight painted them,All work perfect when i am in pose mode,but when i am trying to insert keyframes the objects are moving with no reason in different directions,or they get disappear.Please can you help me because i have stuck and i didnot find any documentation about it

Thank you.

post a blend file.