Bison has at leas two problems with location tracking: empty rhs and error on rhs. A "solution" for the first problem is:

lhs : {@$.first_line = @$.last_line; @$.first_column = @$.last_column; }

A "solution" for the second problem is (you need to do this if reporting error location):

lhs : a b error c {@3.first_line = @2.last_line; @3.first_column = @2.last_column;}