  The Cosmological Principle is part of the foundation that underpins the
standard model of the Universe. In the era of precision cosmology, when stress
tests of the standard model are uncovering various tensions and possible
anomalies, it is critical to check the viability of this principle. A key test
is the consistency between the kinematic dipoles of the cosmic microwave
background and of the large-scale matter distribution. Results using radio
continuum and quasar samples indicate a rough agreement in the directions of
the two dipoles, but a larger than expected amplitude of the matter dipole. The
resulting tension with the radiation dipole has been estimated at $\sim
5\sigma$ for some cases, suggesting a potential new cosmological tension and a
possible violation of the CP. However, the standard formalism for predicting
the dipole in the two-dimensional projection of sources overlooks possible
evolution effects in the luminosity function. In fact, radial information from
the luminosity function is necessary for a correct projection of the
three-dimensional source distribution. Using a variety of current models of the
quasar luminosity function, we show that neglecting redshift evolution can
significantly overestimate the relative velocity amplitude. While the models we
investigate are consistent with each other and with current data, the dipole
derived from these, which depends on derivatives of the luminosity function,
can disagree by more than $3\sigma$. This theoretical systematic bias needs to
be resolved before robust conclusions can be made about a new cosmic tension.
