dont know if this got solved but i have exact same problem.
my mechanic looked into it but couldn't sort the problem,but investigating he found that the starter circuit cut off relay wasn't fully working,he suggested buying a brand new
one in case a secondhand one was defective too.
he isn't sure that this will fix it but it needs to be replaced anyway!if it doesn't fix it at least it rules this line of investigation out.
he checked all the wiring for breaks or shorts ,so we will have to wait till it turns up and is fitted.
oh and i got home with my headlights staying but my tail light was out although the brake light still functioned!good job it was 3am and a quick five mile dash up the road