This behavior occurs in Active Directory and AD LDS, and it's by Microsoft design. AD and AD LDS do not modify the timestamps of an object when there are only some attributes modified. This behavior provokes an issue in the AdminUI and Policy Server cache. When you run XPS tools, you will see the modifications applied in the object, but as the timestamps will not be modified on AD and AD LDS, the AdminUI and the Policy Server cache will not reflect that modification. You need to restart the Policy Server to get the modification applied in the Policy Server cache and thus in the AdminUI.