Here are the scripts from the VIEW SOURCE of my wp-admin login page:
<script type='text/javascript' src='wp-includes/js/...'></script>
<script type='text/javascript' src='wp-includes/js/jquery/...'></script>
<script type='text/javascript' src='http://....com/wp-content/plugins/qr-code-tag/js/jquery.tooltip.min.js?ver=3.2.1'></script>
<script type='text/javascript' src='http://....com/wp-content/plugins/qr-code-tag/js/qrct.js?ver=3.2.1'></script>
<script type='text/javascript' src='wp-content/plugins/.../assets/global.js?ver=1.1'></script>
So, you see that all the other src='' are relative, and the QR Code's src='' is not, since it starts with http://domain.com/... instead of //domain.com/... or wp-content/plugins/...
Please fix. Thank you.