Now that $wgSecureLogin defaults to true for most WMF wikis, Special:UserLogin/signup redirects account creation to https. When it does so it drops all URL parameters to signup apart from returnto and returntoquery.
As a result, we're losing campaign information, and other control over login such as &showGettingStarted=false.
Browse enwiki over http, visit a random page, click Edit, if the yellowish "You are not logged in...." anoneditwarning bar appears, then note the http: link for " or create an account" contains &campaign=anoneditwarning"
But when you click it, you are redirected to
with no campaign parameter.
One fix is to test for campaign and add it back to the $query, in the execute() function in includes/specials/SpecialUserlogin.php. Or, include all query string parameters in the redirect URL.