Multiple MergeDown error

[pahanbi4]

		using (var doc = DocX.Create(@"z:\blah\blah\blah\doc.docx", DocumentType.Document))
		{
			var table = doc.AddTable(5);

			for (int k = 0; k < 10; k++)
			{

				for (int i = 0; i < 5; i++)
				{
					var row = table.AddRow();
					row.SetBorders(Units.HalfPt, BorderValue.Single);

					for (int j = 0; j < 5; j++)
					{
						row.Cells[j].Paragraphs[0].Append($"Cell {(j + 1)}");
					}
				}

				var rows = table.Rows.ToList();

				var c = k * 5;
				var firstRow = rows[c];
				firstRow.Cells[0].MergeRight = 3;
				firstRow.Cells[1].AddParagraph().Append("Should not display.");

				var secondRow = rows[c + 1];
				secondRow.Cells[1].MergeDown = 3;

				var thirdRow = rows[c + 2];
				thirdRow.Cells[1].AddParagraph().Append("Should not display.");
			}

			doc.Save();
			doc.Close();
		}

[pahanbi4]

Hello! I found this error. Maybe I'm using the library incorrectly, but I tried it differently - the result is the same ..