If we are updating means or covariances, keep track of the necessary statistics.

Author: blckmaxima

src/hmmlearn/_emissions.py

@@ -148,7 +148,8 @@ def _accumulate_sufficient_statistics(
                                                   fwdlattice=fwdlattice,
                                                   bwdlattice=bwdlattice)
 
-        if self._needs_sufficient_statistics_for_mean():
+        if self._needs_sufficient_statistics_for_mean() or \
+           self._needs_sufficient_statistics_for_covars():
             stats['post'] += posteriors.sum(axis=0)
             stats['obs'] += posteriors.T @ X