I cannot reproduce.

Can you kill the hung Konqueror process with SIGABRT and paste the backtrace here?

Created an attachment (id=14010) [details]
The page when scrolling

Created an attachment (id=14011) [details]
The page how it should be

It doesn't really hang, it just gets stuck for a second and then continues
again. Or do I get you wrong and you mean something else?
I'm attached 2 pictures. The first one is when I scroll and the second one is
how it actually should be.
BTW: I also noticed that when switching from another tab to a Kubuntu.de tab it
is really slow.

I found a really good example:
http://sagefire.org/C1009907506/E1311212715/index.html

SVN commit 542397 by carewolf:

Only repaint the expossed area when scrolling. 
Fixing local mistakes makes our perfomance less dependent on fully optimized drivers.
BUG: 125580
BUG: 118806


 M  +9 -0      render_box.cpp  


--- branches/KDE/3.5/kdelibs/khtml/rendering/render_box.cpp #542396:542397
@@ -529,7 +529,16 @@
             sy+=b.y()-cy;
             cx=b.x();cy=b.y();cw=b.width();ch=b.height();
         }
+        // restrict painting to repaint-clip
+        if (cy < clipy) {
+            ch -= (clipy - cy);
+            sy += (clipy - cy);
+            cy = clipy;
+        }
+        ch = kMin(ch, cliph);
 
+// 	kdDebug() << " clipy, cliph: " << clipy << ", " << cliph << endl;
+//         kdDebug() << " drawTiledPixmap(" << cx << ", " << cy << ", " << cw << ", " << ch << ", " << sx << ", " << sy << ")" << endl;
         if (cw>0 && ch>0)
             p->drawTiledPixmap(cx, cy, cw, ch, bg->tiled_pixmap(c), sx, sy);