In the recent deployment of HTTPS the users who asked for being redirected to HTTPS are given global forceHTTPS cookies to be redirected to HTTPS on (theoretically) all wiki projects: Wikipedia, Wikisource, etc. In the current setup these global forceHTTPS cookies are set on global domains (.wikipedia.org, etc) but they are prefixed by the original wiki prefix (e.g. frwikiforceHTTPS) or by English-language prefixes (e.g. enwikisourceforceHTTPS), therefore the other language wikis are not redirected to HTTPS.
I guess that this is a bug since some languages (English) are redirected to HTTPS and the others are not, at least it is non-intuitive from a user point of view.
This bug is related to bug 53536 about the absence of removing of the global forceHTTPS cookies in the Wikimedia environment.