Hi,
OOOOK, i found the bug, and i'm sorry for wasting your time and my time
the error is
[Export(typeof(ISubsystemDetailsViewModel))]
[PartCreationPolicy(CreationPolicy.Shared)]
public class SubsystemDetailsViewModel:INotifyPropertyChanged, ISubsystemDetailsViewModel
{...............
that what caused duplication of tabitems.
thank you Adami also thank you DCherubini. now i can sleep .........for today [:)]
