ItemsControl calls IndexOf method of bound collection passing internal class ItemsControl.ItemInfo by Voronin_Pavel

Collection gets the item of wrong type for the IndexOf.

Probably I found the reason for this odd behavior.
Here's the code DataGrid.ScrollIntoView (decompile from Resharper)

internal void ScrollIntoView(ItemsControl.ItemInfo info)
    {
     if (this.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
        this.OnBringItemIntoView(info);
     else
        this.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, (Delegate) new DispatcherOperationCallback(((ItemsControl) this).OnBringItemIntoView), (object) info);
    }

Here you cast info to the object type.
But ItemsControl has two overloads for OnBringItemIntoView:
one for ItemInfo and the second for object type.

internal object OnBringItemIntoView(object arg)
    {
     return this.OnBringItemIntoView(this.NewItemInfo(arg, (DependencyObject) null, -1));
    }

So you get ItemInfo wrapped in ItemInfo. That's why this.LeaseItemInfo(info, true) recieves incorrect item and calls IndexOf with worng value:
info.Index = this.Items.IndexOf(info.Item);