[OU] web page problem - lots of lines when scrolling

[rolf-str at privat.utfors.se]

http://www.orchidehuset.se/

When scrolling with mouse or up/down arrow, I get a lot of horizontal lines on the page. 
Any idea why? I have Opera 9.24. I seem to remember I had that kind of problem with a 
much earlier version of Opera, but I have never had that problem with this version.

Source code is:
<frameset rows="100%">
  <frame src="http://www.orchidehuset.se/joomla/">
</frameset>
<noframes>
  klicka<a href="http://www.orchidehuset.se/joomla/">här</a>!
</noframes>