The full explanation is here:

http://www.jqueryhelp.com/viewtopic.php?t=935

The problem summary:

jQuery strips the <form> tags when returning html with a <form> in it. This is because it is doing a double-innerHTML call. First on the main div that is called from the load, and then for the form tags. This only seems to affect form tags.

I have a snippet of code:

<div id="payform">

<form action="<?php echo $payment_url; ?>" method="post" enctype="multipart/form-data">

<?php if ($fields) { ?>

<?php echo $fields; ?>

<?php } ?>

<input type="submit" value="submit">

</form>

</div>

I use:

$('#payform').load('index.php&action=updatePayment&payment='paypal');

to load a php function and get new output which returns html <form> with new fields and action url:

<form action="https://www.paypal.com/webscr" method="post" enctype="multipart/form-data">

<input type="hidden" name="amount" value="20.00">

<input type="submit" value="submit">

</form>

But the code at line 552:

// Certain attributes only work when accessed via the old DOM 0 way

if ( fix[name] ) {

if ( value != undefined ) elem[fix[name]] = value;

return elem[fix[name]];

} else if ( value == undefined && jQuery.browser.msie && jQuery.nodeName(elem, "form") && (name == "action" || name == "method") )

return elem.getAttributeNode(name).nodeValue;

If I remove that first conditional that uses the "old" way and leave only the "else if" as the new "if". Then the <form> works properly, but I'm not sure if it breaks anything else.