SOLVED
I got on wrong track from decompiling demo parrot which is bound only to bip_spine_3.
In first place it wasn't suppose to be medic item, so I didn't remember to check Archimedes in time :(
For medic it should be bound to bip_collar_L bone.
Hope it will help someone else too.
BTW, anyone knows if there is particular reason why Archimedes is on right shoulder?

Thank you for swift reply... I tried even to skip all jigglebones thing, but it is still the same. Most visible clipping is on crouch and airwalk.
Did I bound it to wrong bip bone (bip_spine_3)?

I made a misc item that is placed on medic left shoulder. I compiled manually with blender SMD tools and my QC, while in ref pose (and some others) everything is fine, jigglebones working etc, but when I play animation, model "sinks" a bit and even changing orientation in some animations. (same behavior is in import tool)
Model has 3 jigglebones and is bound to bip_spine3 and weight mapped.
Position, scale & rotation applied to model and armature
Any ideas what did I miss?