  Scaling properties of galaxy cluster observables with mass provide central
insights into the processes shaping clusters. Calibrating proxies for cluster
mass will be crucial to cluster cosmology with upcoming surveys like eROSITA
and Euclid. The recent Planck results led to suggestions that X-ray masses
might be biased low by $\sim\!40$ %, more than previously considered. We extend
the direct calibration of the weak lensing -- X-ray mass scaling towards lower
masses (as low as $1\!\times\!10^{14}\,\mathrm{M}_{\odot}$) in a sample
representative of the $z\!\sim\!0.4$--$0.5$ population. We investigate the
scaling of MMT/Megacam weak lensing (WL) masses for $8$ clusters at
$0.39\!\leq\!z\!\leq\!0.80$ as part of the \emph{400d} WL programme with
hydrostatic \textit{Chandra} X-ray masses as well as those based on the
proxies, e.g. $Y_{\mathrm{X}}\!=\!T_{\mathrm{X}}M_{\mathrm{gas}}$. Overall, we
find good agreement between WL and X-ray masses, with different mass bias
estimators all consistent with zero. Subdividing the sample, we find the
high-mass subsample to show no significant mass bias while for the low-mass
subsample, there is a bias towards overestimated X-ray masses at the
$\sim\!2\sigma$ level for some mass proxies. The overall scatter in the
mass-mass scaling relations is surprisingly low. Neither observation can be
traced back to the parameter settings in the WL analysis. We do not find
evidence for a strong ($\sim\!40$ %) underestimate in the X-ray masses, as
suggested to reconcile Planck cluster counts and cosmological constraints. For
high-mass clusters, our measurements are consistent with studies in the
literature. The mass dependent bias, significant at $\sim\!2\sigma$, may hint
at a physically different cluster population (less relaxed clusters with more
substructure and mergers); or it may be due to small number statistics.
