  In this study, we present observations of a type Iax supernova, PS1-12bwh,
discovered during the Pan-STARRS1 3$\pi$-survey. Our analysis was driven by
previously unseen pre-maximum, spectroscopic heterogeneity. While the light
curve and post-maximum spectra of PS1-12bwh are virtually identical to those of
the well-studied type Iax supernova, SN 2005hk, the $-$2 day spectrum of
PS1-12bwh does not resemble SN 2005hk at a comparable epoch; instead, we found
it to match a spectrum of SN 2005hk taken over a week earlier ($-$12 day). We
are able to rule out the cause as being incorrect phasing, and argue that it is
not consistent with orientation effects predicted by existing explosion
simulations. To investigate the potential source of this difference, we
performed radiative transfer modelling of both supernovae. We found that the
pre-maximum spectrum of PS1-12bwh is well matched by a synthetic spectrum
generated from a model with a lower density in the high velocity ($\gtrsim$6000
km~s$^{-1}$) ejecta than SN 2005hk. The observed differences between SN 2005hk
and PS1-12bwh may therefore be attributed primarily to differences in the high
velocity ejecta alone, while comparable densities for the lower velocity ejecta
would explain the nearly identical post-maximum spectra. These two supernovae
further highlight the diversity within the SNe Iax class, as well as the
challenges in spectroscopically identifying and phasing these objects,
especially at early epochs.
