https://bugs.freedesktop.org/show_bug.cgi?id=70207
--- Comment #6 from Alex Deucher agd5f@yahoo.com --- It's the same code in the driver whether the console layer calls it or X calls it. Maybe the console also mucks with the backlight? You can use radeonreg (http://cgit.freedesktop.org/~airlied/radeontool/) to compare registers.