The only thing I'm seeing is dimmer problems with an Mk2a using 2.0b11. I have used 2.0b3 and b7 with an Mk2 and this problem didn't exist.

The more I play with it, it seems the dimmer is only a problem when the hard disks are spinning up (ie. at boot time). After that, turning my headlights on and off result in the proper dimmer value.