I have reduced my issue to a simple page with just the code:
<iframe onload=”this.src = lookfor(this);”></iframe>
and a hook (anywhere):
<script type=”text/javascript”>
function lookfor(ifrm) {
ifrm.contentWindow.document.write(“<html><body>Hello world</body></html>”);
}
</script>
It loads “Hello World” as intended — but then shows a Page Not Found error, then refreshes and repeats continuously.
(I tried adding all sorts of src=”” to the iframe, but that doesn’t help)