  The violation of the rotational symmetry constraint of the matrix elements of
the plus component of the vector current, in the Drell-Yan frame, is studied
using an analytical and covariant model of spin-1 composite particle. The
contributions from pair terms or zero modes, if missed cause the violation of
the rotational symmetry. We reanalyze the prescription by Grach and Kondratyuk
to extract form factors which can eliminate theses contributions in particular
models.
