Using the project attached in the internal description try to edit an element and you will get the following in the log:



Telerik.TestStudio.exe(6360:1),TestStudio] <>c__DisplayClass5.<InsertItem>b__4() : EXCEPTION! (see below)
     Outer Exception Type: System.ArgumentOutOfRangeException
     Message: Index must be within the bounds of the List.
          Parameter name: index
     HRESULT: 0x80131502 (Official ID (if app.) = COR_E_ARGUMENTOUTOFRANGE, Error Bit = FAILED, Facility = FACILITY_URT, Code = 5378)
     Call Stack:
          at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
          at System.Collections.Generic.List`1.Insert(Int32 index, T item)
          at System.Collections.ObjectModel.Collection`1.InsertItem(Int32 index, T item)
          at System.Collections.ObjectModel.ObservableCollection`1.InsertItem(Int32 index, T item)
          at Telerik.Windows.Data.RadObservableCollection`1.InsertItem(Int32 index, T item)
          at ArtOfTest.WebAii.Design.ProjectModel.ObservableList`1.<>c__DisplayClass5.<InsertItem>b__4()



You can use this repro video:  http://screencast.com/t/ocAbPlL63Mc