don't work colspan when use .toggle("slow")

don't work colspan when use .toggle("slow")


i need to show the "Subtable" table, when i use only .toggle() it work
fine
but when i use .toggle("slow") , the colspan attribute don't work
anymore.
i don't know if something is missing
thanks for any help.
this is the example
HTML
<table>
    <tr id="mainTable">
        <td>text1</td>
        <td>text2</td>
        <td>text3</td>
        <td>text4</td>
    </tr>
    <tr id="SubTable">
        <td colspan="4">
        <table>
            <tr>
                <td></td>
                <td>text1</td>
                <td>text2</td>
                <td>text3</td>
            </tr>
        </table>
        </td>
    </tr>
</table>
javascript:
$("#SubTable").toggle("slow");