User authentication fails for new users when using delegated authentication directory with auto-add-to-directory enabled

Symptoms as reported by one of the users experiencing this bug:

New users, who have never used Confluence or JIRA before, cannot log in with their Windows account and password. They get a message saying 'Sorry, your username and password are incorrect. Please try again'. When we test the users credentials in the Application 'Authentication Test' we get a 'Successful verification', but the user cannot log in to Confluence or JIRA.

I have found that if I update the Delegated Authentication Directory BASE DN to an invalid value and then reset the same BASE DN to the correct value the users can log in. This seems to only be valid for a short period of time. Eventually any new users attempting to log in are not allowed, getting the same 'Sorry, your username and password are incorrect. Please try again' message.

Nothing helpful in the logs.

Affecting both JIRA and Confluence.

Current workaround is to manually add users to the delegated authentication directory.