also here's what i have done with my character, tell me if i am missing a step somewhere coz of which if could have resulted in that...

1) modeled the character
2) separated head (coz i wanted it like that)
textures
3) set up the skeleton for the entire body (MINUS THE JAW BONE)
4) made a separate bone structure for the tongue and jaw (i had a reference of another character which did the same, and wanted to try that out...)
5) selected the body and head and the all the bones and applied the smooth skin option....(i think i went wrong around here - perhaps in the selection??? )

i wanted to move the jaw and had to work on the paint skin weights...but now that jaw is not moving the way i want it either....(see the attached pics)... which is why i needed to remove the influence, but that resulted in the moved verts...(only for the tongue bone no.3, particularly)....