Th header context menu of the Grid gets closed on click (select/deselect a column) if the Grid is initially scrolled horizontally.

Video: https://www.screencast.com/t/Gm1FLHia


Steps to reproduce:
    1. Open the Live Demos solution for "UI for ASP.NET AJAX R1 2017" in VS2015;
    2. Open the page "UI for ASP.NET AJAX R1 2017\Live Demos\Grid\Examples\Functionality\Scrolling\scrolling\DefaultCS.aspx";
    3. Enable the HeaderContextMenu by setting EnableHeaderContextMenu="True" in the tag telerik:RadGrid;
    4. Disable the column freezing.
    5. Run the Demo and open the page "Grid\Examples\Functionality\Scrolling\scrolling\DefaultCS.aspx";
    6. Scroll the horizontal scrollbar of the grid to the right;
    7. Right click on the column header and pick the Columns from the context menu;
    8. Select or unselect any column, the Column Chooser will close by itself;
    9. Now, scroll the horizontal scrollbar of the grid all the way to the left;
    10. Right click on the column header and pick the Column Chooser from the context menu;
    11. Select or unselect any columns, the Column Chooser won't close by itself.