The [[ view-source:https://store.wikimedia.org/ | source code ]] at the Wikimedia Store includes a canonical URL that points to the non-HTTPS address. There's also a script directly above, that changes to the HTTPS-site.
<script> if (window.location.protocol == "http:") { var restOfUrl = window.location.href.substr(5); window.location.replace("https:" + restOfUrl); } </script> <link rel="canonical" href="http://store.wikimedia.org/" />
At least the canonical URL should be exchanged with the HTTPS address