That makes two of us Peter, please let us know if you find out.
My S4 does the same and also seems to dislike the Ctek charger I was using - which kept going into fault mode. Now using a Halfrauds unit which seems to do the job well. The boot opening button and hazard button both remain faintly illuminated, when the car is off. Techniques say this is "normal" and couldn't find any other obvious drain.
I have tried everything, even trying to talk Mrs R into getting in the boot to see if the light goes off when closed! It does, but I had to video the event myself as my powers of persuasion have obviously declined over the years.
