User is only exported to LDAP when the user's modifiedDate field changed.
When you change the password for a user only, then passwordModifiedDate is updated while modifiedDate is updated only later. Export won't take place because the responsible condition doesn't check for passwordModifiedDate.
1. Build up a Liferay LDAP environment and set LDAP authentication to required
2. Log in with an imported user
3. Update the password of this user in Liferay
4. Try to log in with the new password
User cannot log in. They can log in with the old password though.
User can log in with the new password