We're aware of this problem and working on a solution. What's strange about this is that for some posts we see that HTTP vs HTTPS have separate comments and for some posts they are in sync. Looks like some Disqus problem to me but I haven't had time yet to look deeper into this.
Well, I have the same issue on opera stable. It seems that the light and dark built in themes only change the address bar and the tab bar and nothing more. Even the recently closed tabs menu uses the light theme!
Obviously, it is not related to the dark gtk theme bug. This was solved by forcing opera to use some gtk theme they have made (light grey menus, darker grey selected entries and black letters).