I'm using "AllowCustomSorting" to prevent the RadGrid from sorting the values (they are already sorted) and let it just show the sort direction.
This works fine for "normal" columns.
But if such a column is grouped, the RadGrid ignores this setting and sorts by itself.
In my case it's a column with DateTime values (already formatted as strings) - they are already correctly sorted. But if I group this column, the RadGrid sorts the values itself, and especially for DateTime values as strings, this doesn't work correctly.
How can I prevent the RadGrid from sorting grouped columns and just use them as they are? I'm on the current version (2018.1) of Telerik ASP.NET Ajax.