In a table using HTML markup, if uses rowspan="3" to span downward, then the number of elements in the subsequent two rows is reduced because of the span. However, the template that computes table cell borders named 'html.table.cell.rules' does not check for preceding row spans. It uses this simple test on each cell:
But if there is no following sibling present because the previous cell spans downward, then this test fails, and a cell in the middle of a table does not get its right border. The template needs to keep track of row spans and column positions like the CALS table templates.