Outgoing pre-provisioning task is called for some joined users

In my customer's TEST environment they are seeing AD sAMAccountName being updated for existing users where the join criteria are met.  The only place where the sAMAccountName is set is in the outgoing pre-provisioning task, which should not be called for existing joined entities.

I have also seen a second confirmation that the task is being called for pre-existing users: the "AD Account Creation" notifications being repeatedly sent for a large number of entities every time a Baseline Sync is performed.  The only place where that notification is sent is in that same outgoing pre-provisioning task.