I have a folder on when I click on (left click/right click, doesn't matter) kmail crashes. The backtrace is a little strange, as the crash is in Qt itself. But as I can see this kind of crash only with Kmail and so far only with that folder, I report here.
 The folder is available by request in private mail.

Application: KMail (kmail), signal SIGABRT
[?1034h[Thread debugging using libthread_db enabled]
0x00007f2a5cf28230 in nanosleep () from /lib64/libc.so.6

Thread 1 (Thread 0x7f2a60bfc700 (LWP 5545)):
[KCrash Handler]
#5  0x00007f2a5ceb85c5 in raise () from /lib64/libc.so.6
#6  0x00007f2a5ceb9bb3 in abort () from /lib64/libc.so.6
#7  0x00007f2a5e8e7cdc in qt_message_output () from /opt/qt4/lib/libQtCore.so.4
#8  0x00007f2a5e8e7deb in qFatal () from /opt/qt4/lib/libQtCore.so.4
#9  0x00007f2a5e8e8229 in qt_assert () from /opt/qt4/lib/libQtCore.so.4
#10 0x00007f2a5fa11d98 in addNextCluster () from /opt/qt4/lib/libQtGui.so.4
#11 0x00007f2a5fa140c8 in QTextLine::layout_helper () from /opt/qt4/lib/libQtGui.so.4
#12 0x00007f2a5fa14888 in QTextLine::setLineWidth () from /opt/qt4/lib/libQtGui.so.4
#13 0x00007f2a5f8e8798 in qt_format_text () from /opt/qt4/lib/libQtGui.so.4
#14 0x00007f2a5f8e973a in QPainter::drawText () from /opt/qt4/lib/libQtGui.so.4
#15 0x00007f2a55fe58ce in QPainter::drawText () from /opt/qt4/lib/libQt3Support.so.4
#16 0x00007f2a56052a5e in Q3ListViewItem::paintCell () from /opt/qt4/lib/libQt3Support.so.4
#17 0x00007f2a55332548 in K3ListViewItem::paintCell (this=0x1983a60, p=0x7fff68c5a440, cg=<value optimized out>, column=0, width=535, alignment=1)
    at /data/development/sources/kde-trunk/kdelibs/kde3support/kdeui/k3listview.cpp:2344
#18 0x00007f2a5de6ed7f in KMail::HeaderItem::paintCell (this=0x1983a60, p=0x7fff68c5a440, cg=<value optimized out>, column=0, width=535, align=1)
    at /data/development/sources/kde-trunk/kdepim/kmail/headeritem.cpp:438
#19 0x00007f2a5604c0f3 in Q3ListView::drawContentsOffset () from /opt/qt4/lib/libQt3Support.so.4
#20 0x00007f2a560c3a4c in Q3ScrollView::viewportPaintEvent () from /opt/qt4/lib/libQt3Support.so.4
#21 0x00007f2a55333142 in K3ListView::viewportPaintEvent (this=0x15a9, e=0x15a9) at /data/development/sources/kde-trunk/kdelibs/kde3support/kdeui/k3listview.cpp:1917
#22 0x00007f2a560c413b in Q3ScrollView::eventFilter () from /opt/qt4/lib/libQt3Support.so.4
#23 0x00007f2a5604859c in Q3ListView::eventFilter () from /opt/qt4/lib/libQt3Support.so.4
#24 0x00007f2a5de622d3 in KMHeaders::eventFilter (this=0x11a8b10, o=0x987ab0, e=0x7fff68c5af80) at /data/development/sources/kde-trunk/kdepim/kmail/kmheaders.cpp:284
#25 0x00007f2a5ea07f79 in QCoreApplicationPrivate::sendThroughObjectEventFilters () from /opt/qt4/lib/libQtCore.so.4
#26 0x00007f2a5f7a67f5 in QApplicationPrivate::notify_helper () from /opt/qt4/lib/libQtGui.so.4
#27 0x00007f2a5f7a86a2 in QApplication::notify () from /opt/qt4/lib/libQtGui.so.4
#28 0x00007f2a5f1e3f0b in KApplication::notify (this=0x7fff68c5e450, receiver=0x987ab0, event=0x7fff68c5af80) at /data/development/sources/kde-trunk/kdelibs/kdeui/kernel/kapplication.cpp:311
#29 0x00007f2a5ea0a4c8 in QCoreApplication::notifyInternal () from /opt/qt4/lib/libQtCore.so.4
#30 0x00007f2a5f7b5841 in QCoreApplication::sendSpontaneousEvent () from /opt/qt4/lib/libQtGui.so.4
#31 0x00007f2a5f821e80 in qt_sendSpontaneousEvent () from /opt/qt4/lib/libQtGui.so.4
#32 0x00007f2a5f81b012 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#33 0x00007f2a5f81ba25 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#34 0x00007f2a5f81b8d0 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#35 0x00007f2a5f81b8d0 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#36 0x00007f2a5f81b501 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#37 0x00007f2a5f81ba25 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#38 0x00007f2a5f81b501 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#39 0x00007f2a5f81ba25 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#40 0x00007f2a5f81b8d0 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#41 0x00007f2a5f81b8d0 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#42 0x00007f2a5f81b501 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#43 0x00007f2a5f81ba25 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#44 0x00007f2a5f81b501 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#45 0x00007f2a5f81ba25 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#46 0x00007f2a5f81b501 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#47 0x00007f2a5f81ba25 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#48 0x00007f2a5f81b8d0 in QWidgetPrivate::paintSiblingsRecursive () from /opt/qt4/lib/libQtGui.so.4
#49 0x00007f2a5f81b501 in QWidgetPrivate::drawWidget () from /opt/qt4/lib/libQtGui.so.4
#50 0x00007f2a5f9bf579 in QWidgetBackingStore::cleanRegion () from /opt/qt4/lib/libQtGui.so.4
#51 0x00007f2a5f9bfff1 in qt_syncBackingStore () from /opt/qt4/lib/libQtGui.so.4
#52 0x00007f2a5f811f48 in QWidget::event () from /opt/qt4/lib/libQtGui.so.4
#53 0x00007f2a5fc230f6 in QMainWindow::event () from /opt/qt4/lib/libQtGui.so.4
#54 0x00007f2a5f2e3fd8 in KXmlGuiWindow::event (this=0x15a9, ev=0x15a9) at /data/development/sources/kde-trunk/kdelibs/kdeui/xmlgui/kxmlguiwindow.cpp:125
#55 0x00007f2a5f7a6817 in QApplicationPrivate::notify_helper () from /opt/qt4/lib/libQtGui.so.4
#56 0x00007f2a5f7a86a2 in QApplication::notify () from /opt/qt4/lib/libQtGui.so.4
#57 0x00007f2a5f1e3f0b in KApplication::notify (this=0x7fff68c5e450, receiver=0x119fc60, event=0x1724590) at /data/development/sources/kde-trunk/kdelibs/kdeui/kernel/kapplication.cpp:311
#58 0x00007f2a5ea0a4c8 in QCoreApplication::notifyInternal () from /opt/qt4/lib/libQtCore.so.4
#59 0x00007f2a5f7a38af in QCoreApplication::sendEvent () from /opt/qt4/lib/libQtGui.so.4
#60 0x00007f2a5ea0ab2b in QCoreApplicationPrivate::sendPostedEvents () from /opt/qt4/lib/libQtCore.so.4
#61 0x00007f2a5ea0ae3a in QCoreApplication::sendPostedEvents () from /opt/qt4/lib/libQtCore.so.4
#62 0x00007f2a5f868d9d in QCoreApplication::sendPostedEvents () from /opt/qt4/lib/libQtGui.so.4
#63 0x00007f2a5ea42119 in postEventSourceDispatch () from /opt/qt4/lib/libQtCore.so.4
#64 0x00007f2a5a5b193a in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#65 0x00007f2a5a5b5040 in ?? () from /usr/lib64/libglib-2.0.so.0
#66 0x00007f2a5a5b51dc in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#67 0x00007f2a5ea41226 in QEventDispatcherGlib::processEvents () from /opt/qt4/lib/libQtCore.so.4
#68 0x00007f2a5f8673b7 in QGuiEventDispatcherGlib::processEvents () from /opt/qt4/lib/libQtGui.so.4
#69 0x00007f2a5ea06b5b in QEventLoop::processEvents () from /opt/qt4/lib/libQtCore.so.4
#70 0x00007f2a5ea06d58 in QEventLoop::exec () from /opt/qt4/lib/libQtCore.so.4
#71 0x00007f2a5ea0af49 in QCoreApplication::exec () from /opt/qt4/lib/libQtCore.so.4
#72 0x00007f2a5f7a6574 in QApplication::exec () from /opt/qt4/lib/libQtGui.so.4
#73 0x000000000040304b in main (argc=<value optimized out>, argv=<value optimized out>) at /data/development/sources/kde-trunk/kdepim/kmail/main.cpp:146