As you know, Google is giving a tiny ranking boost to HTTPS URLs.
But I was under the impression the HTTPS URLs must be really secure and that broken/invalid SSL certificates and content mismatch errors would invalidate the ranking boost. I was wrong!
Google’s John Mueller told me in a Google+ Hangout yesterday that Google will currently give the tiny ranking boost even if there are errors, if the URL is HTTPS. He said that may change but right now, since it takes time for webmasters to switch over and deal with the HTTPS/SSL migration quirks, they are being very easy on the requirement.