  A magnetic field parallel to an electrical current does not produce a Lorentz
force on the charge carriers. Therefore, orbital longitudinal magnetoresistance
is unexpected. Here we report on the observation of a large and non saturating
magnetoresistance in lightly doped SrTiO$_{3-x}$ independent of the relative
orientation of current and magnetic field. We show that this quasi-isotropic
magnetoresistance can be explained if the carrier mobility along all
orientations smoothly decreases with magnetic field. This anomalous regime is
restricted to low concentrations when the dipolar correlation length is longer
than the distance between carriers. We identify cyclotron motion of electrons
in a potential landscape tailored by polar domains as the cradle of
quasi-isotropic orbital magnetoresistance. The result emerges as a challenge to
theory and may be a generic feature of lightly-doped quantum paralectric
materials.
