[jQuery] Strange "bold" look after a show in IE6

Hi all,
I'm using animate({opacity: 1});
It produces a strange effect on IE6 where the text appears sort of bold (or sort of duplicated) and a little dirty.
With show() I see this effect during the transition, but when it is finished it looks ok.
With animate({opacity: 1}); it remains "dirty" after the effect.
Anybody experienced this ?
Any know fix or workaround ?
thanks
-Olivier