Change HTTP password problem

We have a number of users that access Domino using POP or IMAP. We use the Administrator client to change user HTTP passwords in the Person document. The problem is that I have noticed that the new password does not work until I remove the person from the ACL on the database, close and the re-add the person to the ACL. Any ideas why that is?

Subject: Server cache

May be because the server not cached the changes yet. Try Dbcache flush.