  We study the radiative transitions between vector and pseudoscalar quarkonia
in the light-front Hamiltonian approach, and investigate the effects of using
different current component and different reference frames. In practical
calculations with truncated Fock spaces, transition form factors may acquire
current component dependence and frame dependence, and such dependences could
serve as a measure for the Lorentz symmetry violation. We suggest using the
transverse current with $m_j=0$ state of the vector meson, since this procedure
employs the dominant spin components of the light-front wavefunctions and is
more robust in practical calculations. We calculate the transition form factor
between vector and pseudoscalar quarkonia and investigate the frame dependence
with light-front wavefunctions calculated from the valence Fock sector. We
suggest using frames with minimal longitudinal momentum transfer for
calculations in the valence Fock sector, namely the Drell-Yan frame for the
space-like region and a specific longitudinal frame for the timelike region; at
$q^2=0$ these two frames give the same result.
