Headlight malfunction dash warning

Hi all

I have recently bought a 2010 Mondeo Titanium x TDCI and up to now am well pleased with it, in fact, I love it, after having driven BMW (3 series) Audi A4 and Citroen C5, I can safely say, it`s the best of all up to now, any way, 1 annoying little thing is at night with the lights on, I sometimes get a headlight malfunction warning (a little yellow light in the dash) the headlights still work but, don`t seem to do the "adaptive" bit any more, normally when I stop at lights etc, the headlights do a kind of reset lol, sort of move left and right and settle again, but they don`t do this when the warning light is on, if I switch the engine off, then start up again, all works fine, till a few weeks later and it happens again, any ideas what it could be? Rob