workgroup manager preferences problem

In Workgroup Manager the Mobility preference isn't working right.

At the media departement we have two MacMini server's with Lion Server 10.7.5.

One server is OD master and the second is OD replicate. The server is bound in AD and all is connected through the "Golden Triangle".

The iMac's at the department are connected in AD and OD so the students can log in with their AD credentials and de iMac's get the preferences via OD.

The problem is that when the students log out of their account we want this account to be deleted from the iMac so there the machines stay as clean as possible.

The settings we've used in the mobility preferences are the following:

Tab Account creation, always:

v Create Mobile account when user logs in to network account (checked)

- Require confirmation before creating mobile account (not checked)

Create home using:

Local home template

Tab Account expiry, always:

v Delete mobile accounts 0 hours after user's next login (checked)

- Delete only after succesful sync (unchecked)

Does anyone encounter the same problems?