Autocad to pdf solid fill issue

Hi

I don't very often use solid fills but noticed recently when I pdf'ed a drawings containing solid fill that the subsequent pdf (viewing in acrobat 7 & 8 - I have not tried earlier versions) shows the solid fill with a visible diagonal dashed line across the fill, which I presume reflects autocads internal island analysis of the filled shape.

In acrobat reader 8, under Preferences- Rendering if I untick 'smooth line art' the diagonal dashed lines disappear, however, I then loose smoothness of any curved lines within the drawings.

I have also noticed the same thing in other pdf'd autocad drawings on the web, an example of the type of thing that I am talking about can be found at:

Can these dashed lines be controlled/omitted from within autocad?

Thanks