Crash in Webkit sample browser

Stacktrace follows.

Have not been able to find a reproducible scenario, but error occurs with some frequency during random web surfing.

Log:

ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ERROR: called FrameView::paint with nil renderer
page\FrameView.cpp(3570) : WebCore::FrameView::paintContents
ASSERTION FAILED: m_repaintRect == renderer()>clippedOverflowRectForRepaint(renderer()>containerForRepaint())
c:\qt520a\qtwebkit\source\webcore\rendering\RenderLayer.cpp(809) : WebCore::RenderLayer::updateLayerPositionsAfterScroll

Stacktrace:

0 WTFCrash Assertions.cpp 339 0x52b97567
1 WebCore::RenderLayer::updateLayerPositionsAfterScroll RenderLayer.cpp 810 0x51d3adeb
2 WebCore::RenderLayer::updateLayerPositionsAfterDocumentScroll RenderLayer.cpp 761 0x51d3abac
3 WebCore::FrameView::repaintFixedElementsAfterScrolling FrameView.cpp 2050 0x51caf00c
4 WebCore::ScrollView::scrollTo ScrollView.cpp 398 0x51f0ca06
5 WebCore::FrameView::scrollTo FrameView.cpp 3092 0x51cb1cba
6 WebCore::ScrollView::setScrollOffset ScrollView.cpp 379 0x51f0c949
7 WebCore::ScrollableArea::scrollPositionChanged ScrollableArea.cpp 147 0x51f16dbf
8 WebCore::ScrollableArea::setScrollOffsetFromAnimation ScrollableArea.cpp 191 0x51f16fbc
9 WebCore::ScrollAnimator::notifyPositionChanged ScrollAnimator.cpp 143 0x5232d815
10 WebCore::ScrollAnimator::scrollToOffsetWithoutAnimation ScrollAnimator.cpp 82 0x5232d3de
11 WebCore::ScrollableArea::scrollToOffsetWithoutAnimation ScrollableArea.cpp 125 0x51f16cb5
12 WebCore::ScrollView::updateScrollbars ScrollView.cpp 637 0x51f0dc1b
13 WebCore::ScrollView::setScrollPosition ScrollView.cpp 437 0x51f0cbb7
14 WebCore::FrameView::setScrollPosition FrameView.cpp 1969 0x51caecc8
15 WebCore::RenderLayer::scrollRectToVisible RenderLayer.cpp 2360 0x51d3f74f
16 WebCore::RenderLayer::scrollRectToVisible RenderLayer.cpp 2371 0x51d3f7c0
17 WebCore::RenderLayer::scrollRectToVisible RenderLayer.cpp 2371 0x51d3f7c0
18 WebCore::RenderLayer::scrollRectToVisible RenderLayer.cpp 2371 0x51d3f7c0
19 WebCore::RenderLayer::scrollRectToVisible RenderLayer.cpp 2371 0x51d3f7c0