Unfortunately, this is a MIUI HTC One X bug that came in when they moved up to Jelly Bean. It was really annoying when I upgraded to JB, but I've gotten kinda used to it. A fix would be great though.
Wow, I didn't expect that to actually work - thanks! For anyone else, I needed to reboot after applying the status bar theme before the lag went away. The toggles are now green, but I can definitely live with that.
Cheers, Alex =)