Alias does not recognize taxonomy reversion to "none selected" after bulk delete/generate

This bug can be replicated thus: A vocabulary of two terms, "About" and "Mission", was created, and automated alias settings having the default pattern [termpath-raw]/[title-raw] were configured. Additionally, two pages having the titles "About" and "Mission" were created. Selecting the term "About" for the taxonomy of the "About" page yields an alias of about/about, as expected. The "Mission" page holds the "None selected" option, and its alias is, as expected, mission.

However, on the "About" page, reverting back to the option "None selected" and then saving does not affect the alias about/about. The alias remains about/about even when the alias should be simply about. "None selected" should nullify the [termpath-raw] token as it did on the "Mission" page. Bulk deleting all aliases and regenerating them does not change the "About" alias, even after re-saving the page.