The javascript to focus on the login box seems to be the problem indeed.
This piece of js is causing it:
<script type="text/javascript">
if (document.loginfrm) document.loginfrm.username.focus();
</script>
In the source code it shows right under the loginreminder form, might be worth checking out your form chunks.
If you didn’t use a chunk for the form, find the default one, probably in /assets/snippets/snippetname somewhere, depending on the snippet you use.