QGraphicsItem scrolling always invalidates full scene in cached mode (exposedRect always has full item area)

QGraphicsItem scrolling always invalidates full scene if item in cached mode (setCacheMode(QGraphicsItem::ItemCoordinateCache)).
This makes scrolling slower (especially of QGraphicsWebView on big pages), because paint method has to repaint the whole page.

Reason on Symbian:
In cached part of scroll method call to d->scene->d_func()->markDirty(this) invalidates the whole scene. This call is not necessary, because this code
foreach (QRect rect, exposed.rects())
update(rect);
calls the same markDirty with correct rect (like d->scene->d_func()->markDirty(this, rect)).

Patch that fixes this on Symbian:
— qgraphicsitem.cpp.old 2010-02-19 17:54:30.000000000 -0500
+++ qgraphicsitem.cpp 2010-02-19 16:23:22.000000000 -0500
@@ -5461,7 +5461,7 @@
exposed -= r.translated(dx, dy);
foreach (QRect rect, exposed.rects())
update(rect);

• d->scene->d_func()->markDirty(this);
  +// d->scene->d_func()->markDirty(this);
  } else { update(rect); }

On linux there is another problem in cached scrolling: QPixmapCache::find never able to find cached pixmap because c->key is invalid .

Test application attached.