Both filter_performers and filter_engravers used to use a direct dynamic_cast
on the unsmobbed translator to be filtered, i.e.,
- if (dynamic_cast<Performer *> (Translator::unsmob (scm_car (*tail))))
+ if (Performer::unsmob (scm_car (*tail)))
but this caused mysterious optimisation issues in several GUB builds. See
issue #818 for the background to this change.