If you add the following content in the Wiki Editor (not WYSIWYG)
<td colspan="2"> Test </td>
And then edit it using the WYSWIYG Editor it will be transformed from a custom HTML Table to a Wiki Table. The colspan will be lost in the process and the table will look quite dirrently.
We need to "tag" the manual tables when converting to the WYSIWYG Editor so that they are not converted on saving. You can add anything in the TABLE tag that will allow you do detect it on saving.