Never mind, I know what the issue is. You have installed Column Divider Pro, which puts the grid into tables so it can work reliably for all browsers, even old IE versions.
Code:
<td class="vDotLine" rowspan="2"></td>
The tables are no longer required for any modern browser; I tried rewriting it to use divs with CSS instead of tables a few years ago, but IE was still not up to speed and would have required extensive (javascript, which I do not know much of) special handling to make it work.