  We present results of measurements of electrical, magnetic and thermal
properties of EuB$_{5.99}$C$_{0.01}$. The observed anomalously large negative
magnetoresistance as above, so below the Curie temperature of ferromagnetic
ordering $T_C$ is attributed to fluctuations in carbon concentration. Below
$T_C$ the carbon richer regions give rise to helimagnetic domains, which are
responsible for an additional scattering term in the resistivity, which can be
suppressed by a magnetic field. Above $T_C$ these regions prevent the process
of percolation of magnetic polarons (MPs), acting as "spacers" between MPs. We
propose that such "spacers", being in fact volumes incompatible with existence
of MPs, may be responsible for the decrease of the percolation temperature and
for the additional (magneto)resistivity increase in systems with MPs.
