[Zope] Nothing in undo list

I created a folder and added a acl_users. When a user from this acl_users logs in and manipulates things in Zope and Plone he can not see anything in the undo_list. If I enter as a user that is declared in the root acl_users he can see and undo all the manipulations. Both of this users are managers. What could be the reason for this.? What sould I do that everyone can undo his/her modifications? thanks Robert