As I understand you use a Converter for the column binding. The IValueConverters are for UI purposes. They do not take part in our data engine when it comes to filtering, sorting and so on. Our data engine operates over the "raw" data, i.e. it does not pass it through the IValueConverter. The IValueConverter is only used to display the raw data to the end-user, i.e. in the grid cells or in the distinct values list.
If you apply a converter for the columns, it will be applied to the filter distinct values as well. So the distinct values will be the same as shown in the GridViewDataColumn. I do not understand why do you need to get the distinct values that return all the country names. Am I missing something?
All the best,
the Telerik team
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