  We illustrate, using a simple model, that in the usual formulation the
time-component of the Klein-Gordon current is not generally positive definite
even if one restricts allowed solutions to those with positive frequencies.
Since in de Broglie's theory of particle trajectories the particle follows the
current this leads to difficulties of interpretation, with the appearance of
trajectories which are closed loops in space-time and velocities not limited
from above. We show that at least this pathology can be avoided if one uses a
covariant extension of the canonical formulation of relativistic point particle
dynamics proposed by Gitman and Tyutin.
