Thanks for your time and interest in helping the jQuery project. We require that all bugs have a working, reproducible testcase on jsFiddle or another working live demo so that we can audit the bug further. If you can provide that, we can investigate this potential issue further. Thank you.

Replying to [comment:1 ajpiano]:

Thanks for your time and interest in helping the jQuery project. We require that all bugs have a working, reproducible testcase on jsFiddle or another working live demo so that we can audit the bug further. If you can provide that, we can investigate this potential issue further. Thank you.

This problem concerning Internet Explorer ONLY, i tried it on jsFiddle but it can't be reproduced there.

Try to put this code in Internet Explorer 7 or 8:

$(document).ready( function () {
      $(window).bind("load", function() {
            $("My selector does not exist").replaceWith("My new content");
      });
});

it was working on Firefox.

Other functions such as append(), html(), etc work fine on non existing selectors.

The fact that this cannot be duplicated in jsFiddle (http://jsfiddle.net/Y779e/) or jsBin (http://jsbin.com/ezaxu4) in IE means that we cannot move forward in diagnosing this potential issue. If you can provide us with a test page in some format, then we may be able to assist - if not, we can't.

For what it's worth, the first line of replaceWith in the jQuery source checks to make sure that there are elements in the wrapped set:

        replaceWith: function(value) {
            if (this[0] && this[0].parentNode) {

sorry i m not used to your tools and not realy concentrated, so here is my problem for all browser in fact :

http://jsbin.com/ezaxu4/3/

$("h2 sup").replaceWith('®');

error: uncaught exception: Syntax error, unrecognized expression: ®

it seems only that not very good for coding ...

Sorry for the noize

.replaceWith is not designed to support replacing an element with an arbitrary string - it requires an element, an HTML string representing an element, or a jQuery object.