表单提交问题IE9 + Ajax

Question

I have a form that is served via Ajax from the server when a button is clicked. It pops up in a jquery dialog.

<form onsubmit="hideModal();return getAJAX(this);">
    <input type="hidden" name="action" value="updateUserNotes">
    <input type="hidden" name="userid" value="20312">
    <hr/>
    <B>Flags:</B><BR/>
    <input type="radio" name="flag" value="none" checked> <img src="images/icons/grey_flag.png"> No Flag<BR>
    <input type="radio" name="flag" value="green"  > <img src="images/icons/flag_green.png"> Green Flag<BR>
    <input type="radio" name="flag" value="red" > <img src="images/icons/flag_red.png"> Red Flag

    <B>NOTES:</B><BR>
    <textarea name="usernotes" cols="80" rows="10"></textarea>
    <input type="submit" value="Save Notes">
</form>

This is the code that my script sends back to display the form. With the HR in there, the form will not submit when you click "save notes". It does not throw a javascript error, it simply does not submit.

If I remove the horizontal rule the form submits 100% fine.

Anyone know what might be causing this? It only appears to affect IE9. I cannot replicate it in Chrome or Firefox or earlier versions of IE9.

I think it has something to do with IE9's strictness, but I can't figure out how the horizontal rule is messing anything up.