An other strange thing is that the "button illumination level" is not working for 100% anymore. I can readjust it what I want but it only shows '6' or 'MAX'


Can you clarify what you mean by this? MAX=100% when the headlights are off, and one step less when they are on. (Unless your car inverts it's dimmer line, in which case, reverse the above statement!)

The problem with the buttons in car mode is due ( I believe) to a race hazard between the player changing the display brightness, and the button LED code changing the button brightness. Both the button and display brightness are handled by the same PIC, and this PIC takes about 0.1 seconds to process a command...it's something I'm trying to find time to look into..I don't understand why it doesn't happen in AC mode though.

Can you try turning your headlights on and off, and see what happens?