cause its a plastic lense. my mums punto does it, and my clio does it occasionally.
[Edited by Middo on 10 February 2005 at 12:26pm]
fiat dealership told my mum there was nothing to worry about unless you had water visibly dripping down the inside of the lens. my clios seem to fog up, but it quickly disappers when the engines been on or if it warms up.