Quote:

Do dictionaries exhibit bias by not mentioning the negative connotation of the term?



Maybe so, Jon. AHD4 and W3 both omit the pejorative sense; but OED2 covered it:

tar-baby, (a) the doll smeared with tar, set to catch Brer Rabbit (see quot. 1881); hence transf., spec. an object of censure; a sticky problem, or one which is only aggravated by attempts to solve it (colloq.); (b) a derog. term for a Black (U.S.) or a Maori (N.Z.) [E.A.]