Version:            (using KDE Devel)
Installed from:    Compiled sources

The attached testcase has a primary ('fancy') and an alternate ('plain') stylesheet. In the primary stylesheet a div element is set to float, and in the alternate, it's not mentioned. Switching primary => alternate causes the crash:

[New Thread 16384 (LWP 8746)]
0x41297bb8 in waitpid () from /lib/libpthread.so.0
#0  0x41297bb8 in waitpid () from /lib/libpthread.so.0
#1  0x409f7bc8 in __JCR_LIST__ () from /home/tla/kde-cvs/lib/libkdecore.so.4
#2  0x40934979 in KCrash::defaultCrashHandler(int) (sig=6) at kcrash.cpp:246
#3  0x412967f5 in __pthread_sighandler () from /lib/libpthread.so.0
#4  <signal handler called>
#5  0x414d5561 in kill () from /lib/libc.so.6
#6  0x41293741 in pthread_kill () from /lib/libpthread.so.0
#7  0x41293a4b in raise () from /lib/libpthread.so.0
#8  0x414d5314 in raise () from /lib/libc.so.6
#9  0x414d6828 in abort () from /lib/libc.so.6
#10 0x414cea5f in __assert_fail () from /lib/libc.so.6
#11 0x4205d4fc in khtml::RenderBlock::createLineBoxes(khtml::RenderObject*) (
    this=0x82ad230, obj=0x82ad310) at bidi.cpp:445
#12 0x4205d776 in khtml::RenderBlock::constructLine(khtml::BidiIterator const&, khtml::BidiIterator const&) (this=0x82ad230, start=@0xbfffe8c0, 
    end=@0xbfffe8b0) at bidi.cpp:491
#13 0x4205f333 in khtml::RenderBlock::layoutInlineChildren(bool) (
    this=0x82ad230, relayoutChildren=false) at bidi.cpp:1223
#14 0x420630c4 in khtml::RenderBlock::layoutBlock(bool) (this=0x82ad230, 
    relayoutChildren=false) at render_block.cpp:498
#15 0x42062cca in khtml::RenderBlock::layout() (this=0x82ad230)
    at render_block.cpp:418
#16 0x42064437 in khtml::RenderBlock::layoutBlockChildren(bool) (
    this=0x82ad1bc, relayoutChildren=false) at render_block.cpp:822
#17 0x420630d9 in khtml::RenderBlock::layoutBlock(bool) (this=0x82ad1bc, 
    relayoutChildren=false) at render_block.cpp:500
#18 0x42062cca in khtml::RenderBlock::layout() (this=0x82ad1bc)
    at render_block.cpp:418
#19 0x420b1b7c in khtml::RenderBody::layout() (this=0x82ad1bc)
    at render_body.cpp:92
#20 0x42064437 in khtml::RenderBlock::layoutBlockChildren(bool) (
    this=0x82ad104, relayoutChildren=false) at render_block.cpp:822
#21 0x420630d9 in khtml::RenderBlock::layoutBlock(bool) (this=0x82ad104, 
    relayoutChildren=false) at render_block.cpp:500
#22 0x42062cca in khtml::RenderBlock::layout() (this=0x82ad104)
    at render_block.cpp:418
#23 0x42064437 in khtml::RenderBlock::layoutBlockChildren(bool) (
    this=0x82ad020, relayoutChildren=false) at render_block.cpp:822
#24 0x420630d9 in khtml::RenderBlock::layoutBlock(bool) (this=0x82ad020, 
    relayoutChildren=false) at render_block.cpp:500
#25 0x42062cca in khtml::RenderBlock::layout() (this=0x82ad020)
    at render_block.cpp:418
#26 0x420aa32a in khtml::RenderCanvas::layout() (this=0x82ad020)
    at render_canvas.cpp:168
#27 0x41faff12 in KHTMLView::layout() (this=0x834b670) at khtmlview.cpp:579
#28 0x41fb65b0 in KHTMLView::timerEvent(QTimerEvent*) (this=0x834b670, 
    e=0xbffff300) at khtmlview.cpp:2160
#29 0x40d0eb7b in QObject::event(QEvent*) ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#30 0x40d3edf6 in QWidget::event(QEvent*) ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#31 0x40cbf20d in QApplication::internalNotify(QObject*, QEvent*) ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#32 0x40cbe950 in QApplication::notify(QObject*, QEvent*) ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#33 0x408ac8fd in KApplication::notify(QObject*, QEvent*) (this=0xbffff6f0, 
    receiver=0x834b670, event=0xbffff300) at kapplication.cpp:505
#34 0x40cb0113 in QEventLoop::activateTimers() ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#35 0x40c7372e in QEventLoop::processEvents(unsigned) ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#36 0x40ccec13 in QEventLoop::enterLoop() ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#37 0x40ccead0 in QEventLoop::exec() ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#38 0x40cbf428 in QApplication::exec() ()
   from /home/tla/kde-cvs/lib/libqt-mt.so.3
#39 0x400726e9 in kdemain (argc=2, argv=0xbffff844) at konq_main.cc:184
#40 0x08048647 in main ()