Exception when casting from {{DisconectedItem}} to Collection Type

[Yuki-Codes]

If the treeview contents are changed during MouseDown an Exception is thrown when the mouse is released.

SelectionMultiple.OnMouseUp(MousebuttonEventArgs) [Line 267] Should probably check if the selectItem.DataContext has been set to a DisconnectedSource before attempting to select the item.

In .Net 4.5+ this can be done with if (selectItem.DataContext == BindingOperations.DisconnectedSource) however in earlier .NET versions the only way to check is with a string compare like if ((string)selectItem.DataContext == "{{DisconectedItem}}")

[nkast]

Is there an easy way to reproduce this? Preferably from within one of the existing samples.
I guess this happens when the selected item(s) is removed from the list, right?

I would prefer to keep supporting the .net 4.0 framework or find a better solution to this, for example check if the items is still part of the list or update the state of SelectionMultiple when the tree changes and items are removed.