I have found the solution myself now. It can be found using this link: http://forum.jquery.com/topic/is-jquery-stripping-form-tags
What I did is exchange the jQuery call with this one here:
$.get("/link/to/html/file/with/form/file.htm", function (data) {
$("#myForm")
.html('')
.append(data);
});
It seems that the .html I used above strips out the form tag. I don't know if it's a problem with IE or with jQuery but if I use the $.get instead the $.load and .append instead of .html, it works.
Hope this helps.