IMO this is not an intended behaviour for non-adminsitrators. Would you please be so kind to log it into the public issue tracker at support.dotnetnuke.com, thank you.

Someone with some usability thoughtfulness such as yourself and Alex should take a serious look at this Sebastian.

The control panel , mode : view | edit , design ( used to be preview ), keeps getting more and more convulted. 

How can any casual user figure all this out?

What is worse is that the code to support all of this is just keeps tying itself in knots.

Here are just a couple examples

This statement if from just one place that decides if the control panel should be shown. 

This happens on every request:

Or how about this one that is called for every title on every module in the page:

blnCanEdit = (PortalSettings.UserMode = PortalSettings.Mode.Edit)

AndAlso (PortalSecurity.IsInRoles(PortalSettings.AdministratorRoleName) OrElse PortalSecurity.IsInRoles(PortalSettings.ActiveTab.AdministratorRoles.ToString)) AndAlso (IsAdminControl() = False) AndAlso (PortalSettings.ActiveTab.IsAdminTab = False)