Log Hours UI hangs when saving a row added via the "Add Volunteer" button

The problem doesn't appear to affect activities that were added via another interface (e.g., Assign Volunteers). Only records added ad hoc to this screen exhibit the behavior.

Error message: Mandatory key missing from params array: id or volunteer_need_id.

Backtrace suggests CRM_Volunteer_BAO_Assignment::createVolunteerActivity() is throwing the error. It would seem the newly created rows need a little extra help with context since, unlike the other rows on the page, the new records cannot refer to an existing activity ID.