We demonstrate that the reciprocal-space Hamiltonian method for quanti
zing the electromagnetic fields in a dispersive dielectric medium lead
s to inconsistencies when applied to the cases of plasmon polaritons a
nd coupled phonon-plasmon polaritons. In particular, we show that the
use of the standard expressions for the dielectric functions in these
two cases leads to the violation of the Huttner-Barnett velocity-ratio
sum rule and, hence, to the breakdown of the equal-time canonical fie
ld commutation relations. We show that correct behavior is recoverable
after the dielectric functions are appropriately regularized. Regular
ization effectively leads in each case to the introduction of an addit
ional transverse low-frequency polariton branch. This is sufficient to
rectify the theory and there is no need to invoke the presence of the
longitudinal modes. The theory is illustrated with reference to the c
oupled phonon-plasmon polaritons of Si-doped GaAs.