You can work this around by setting the PreservePositionWhenMaximized to False and implement custom preserving logic. You can see this approach in the attached project.

private bool isManualPositionChanged = false;
private Dictionary<RadTileViewItem, int> maximizedItemPositionCache = new Dictionary<RadTileViewItem, int>();

public MainWindow()
{
	InitializeComponent();
	this.xTileView.PreviewTileStateChanged += XTileView_PreviewTileStateChanged;
}

private void XTileView_PreviewTileStateChanged(object sender, Telerik.Windows.Controls.PreviewTileStateChangedEventArgs e)
{
	if (this.isManualPositionChanged)
            {
                return;
            }

            RadTileViewItem tileViewItem = (RadTileViewItem)e.OriginalSource;
            var header = tileViewItem.Header;
            TileViewItemState oldState = e.TileState;
            TileViewItemState newState = tileViewItem.TileState;

            if (newState == TileViewItemState.Minimized || newState == TileViewItemState.Restored)
            {
                if (maximizedItemPositionCache.ContainsKey(tileViewItem))
                {
                    this.isManualPositionChanged = true;
                    tileViewItem.Position = maximizedItemPositionCache[tileViewItem];
                    this.isManualPositionChanged = false;
                    maximizedItemPositionCache.Remove(tileViewItem);
                }
                if (newState == TileViewItemState.Restored)
                {
                    this.isManualPositionChanged = true;
                    var tileView = sender as RadTileView;
                    foreach (RadTileViewItem item in tileView.Items)
                    {
                        if (item.TileState == TileViewItemState.Maximized)
                        {
                            item.TileState = TileViewItemState.Restored;
                        }
                    }
                    this.isManualPositionChanged = false;
                }
            }
            else if (newState == TileViewItemState.Maximized)
            {
                if (!maximizedItemPositionCache.ContainsKey(tileViewItem))
                {
                    maximizedItemPositionCache[tileViewItem] = tileViewItem.Position;
                }
            }
}