I experimented quite a bit with this and it really is a weird problem. When viewing the source using IE 9 dev tools with ie8 browser mode it looks like the divRight has been moved into a span that is part of the NeatUpload progress bar. It also seems like an Artisteer thing they way they use display:table; and lots of table-layout:table-row and table-layout.tablecell seems to also be a factor. It works correctly in the jqueryui-1 skin in my testing.
And I'm able to solve it again somewhat by overriding some artisteer css for ie8 by adding this in style-artisteer-overrides.css:
.ie8 .art-content-layout
{
table-layout: inherit;
}
this is changing it from table-layout:table that artisteer is adding back to the default inherit.
this fixed the layout except for the layout column background colors still seem to be not distributed correctly (I'm testing with artisteer31-green not sure it it affects others).
I really don't know what else to try to solve it any better than this mainly because I don't really understand the cause of the problem,.
Best,
Joe