I think, this is an important bug. Process any refentry and the resulting man-page will contain:
foo - does this
foo \- does this
The comment in the refnamediv template says, that the minus will be replaced by the apply-string-subst-map. But this doesn't happen. I did not yet examine, why not (maybe a regression from the change-back from 1.72 to 1.73?). Reproducible in the snapshot too.