C# Excel refactoring code gives different result

Starting with a string representing a range:

string sortRange = "C10:H24";

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This then works:

worksheet.Range[sortRange].Sort(worksheet.Range[sortRange].Columns[1], xlSortOder.xlDescending);

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I saw worksheet.Range[sortRange] was listed twice, so I decided to refactor that out:

Excel.Range r = worksheet.Range[sortRange];
Excel.Range c = r.Columns[1];
r.Sort(c, xlSortOrder.xlDescending);

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My refactored version gives a much different result. Why is that?