When a Table consisting of one TableRow that contains a TableCell with a Rowspan > 1 set, additional lines are added to the table.
Table table = new Table();
TableRow row = table.Rows.AddTableRow();
row.Cells.AddTableCell();
TableCell secondCell = row.Cells.AddTableCell();
secondCell.RowSpan = 2;
table.Measure();
table.Rows.AddTableRow();