Chrome renders this markup incorrectly (see jsfiddle for full markup).
table { border-collapse: collapse }
Here it is in Chrome:
According to Chrome bug with colspan and border?, this is a Chrome bug since 2008... which is not fixed yet.
One workaround for this issue is: not use colspan
. Sample code is:
<tr>
<td class=A>1</td>
<td class=A>2</td>
<td class=A>3</td>
<td></td>
<td></td>
<td></td>
</tr>
instead of
<tr>
<td class=A>1</td>
<td class=A>2</td>
<td class=A>3</td>
<td colspan=3></td>
</tr>
fiddle for your example.
Or, you can use mistermansam's workaround by abandon border-collapse
.