I think I found a bug wich need fixing. Not sure if this the right place to put this, but here it comes.
A client of mine using the sitebuilder made her site and looked fine in the WYSIWYG editor. Fonts were right, text was fine and images were all displayed. But when trying to preview the site, the site didn't show. It showed an empty page. Looking in at the files in the preview directory, all html files were empty. Also the publishing didn't work.
I started a new project and copying every page one by one, and i found the problem. The id in the img tag can cause problems.
In the WYSIWYG editor in html mode the img:
<img id="_x0000_i1090" height="144" alt="" src="http://funhuispagina.sytes.net/animaties/animaties/ham56.gif" width="433" />
Is causing problems. Changed it to:
<img id="x0000i1090" height="144" alt="" src="http://funhuispagina.sytes.net/animaties/animaties/ham56.gif" width="433" />
And now everything works perfect again. Possible to preview again and to publish the site. I changed the id back to the original, with the _ in the id. And again not possible to preview and to publish. So there seems to go something wrong.
Hope this help others with the same sort of problem.