When the ItemsPanel is set to VirtualizingStackPanel which Orientation is set to Horizontal, selecting an item moves it to the rightmost position. Available in LIB version 2016.3.1017, it will be also available in the 2016 R3 SP1 release.
The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.