[Zope] Nothing in undo list

[robert rottermann]

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