Application that crashed: kontact
Version of the application: 4.3.1
KDE Version: 4.3.1 (KDE 4.3.1)
Qt Version: 4.5.2
Operating System: Linux 2.6.27.30-170.2.82.fc10.x86_64 x86_64
Distribution: "Fedora release 10 (Cambridge)"

What I was doing when the application crashed:
I'm pretty sure I'm hitting this same problem. I can reproduce it pretty readily.  Anytime, I attempt to forward or send an e-mail (as opposed to replying without adding new e-mail addresses) Kontact will segfault pretty quickly while apparently attempting to perform and LDAP address lookup (when I'm working in offline mode).

 -- Backtrace:
Application: Kontact (kontact), signal: Segmentation fault
[KCrash Handler]
#5  QListWidgetItem::text (this=0x0) at /usr/include/QtGui/qlistwidget.h:90
#6  0x00007f23d4d2fb7c in KPIM::AddresseeLineEdit::slotLDAPSearchData (this=<value optimized out>, adrs=<value optimized out>) at /usr/src/debug/kdepim-4.3.1/libkdepim/addresseelineedit.cpp:820
#7  0x00007f23d4d30b2c in KPIM::AddresseeLineEdit::qt_metacall (this=0x32cc240, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fffd9bef9f0)
    at /usr/src/debug/kdepim-4.3.1/x86_64-redhat-linux-gnu/libkdepim/addresseelineedit.moc:95
#8  0x00007f23c3adc42d in KMLineEdit::qt_metacall (this=0x7fffd9bef840, _c=QMetaObject::InvokeMetaMethod, _id=29003760, _a=0x1)
    at /usr/src/debug/kdepim-4.3.1/x86_64-redhat-linux-gnu/kmail/kmlineeditspell.moc:68
#9  0x00007f23c3b4dc3d in RecipientLineEdit::qt_metacall (this=0x7fffd9bef840, _c=QMetaObject::InvokeMetaMethod, _id=29003760, _a=0x1)
    at /usr/src/debug/kdepim-4.3.1/x86_64-redhat-linux-gnu/kmail/recipientseditor.moc:123
#10 0x000000302bb58f52 in QMetaObject::activate () from /usr/lib64/libQtCore.so.4
#11 0x00007f23d4d33905 in KPIM::LdapSearch::searchData (this=0x7fffd9bef840, _t1=<value optimized out>) at /usr/src/debug/kdepim-4.3.1/x86_64-redhat-linux-gnu/libkdepim/ldapclient.moc:205
#12 0x00007f23d4d36a21 in KPIM::LdapSearch::slotDataTimer (this=0x20dace0) at /usr/src/debug/kdepim-4.3.1/libkdepim/ldapclient.cpp:465
#13 0x00007f23d4d36aa5 in KPIM::LdapSearch::finish (this=0x20dace0) at /usr/src/debug/kdepim-4.3.1/libkdepim/ldapclient.cpp:472
#14 0x00007f23d4d39408 in KPIM::LdapSearch::qt_metacall (this=0x20dace0, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fffd9befb10)
    at /usr/src/debug/kdepim-4.3.1/x86_64-redhat-linux-gnu/libkdepim/ldapclient.moc:184
#15 0x000000302bb58f52 in QMetaObject::activate () from /usr/lib64/libQtCore.so.4
#16 0x00007f23d4d33ff9 in KPIM::LdapClient::slotDone (this=0x20df0c0) at /usr/src/debug/kdepim-4.3.1/libkdepim/ldapclient.cpp:119
#17 0x00007f23d4d39b50 in KPIM::LdapClient::qt_metacall (this=0x20df0c0, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fffd9befcb0)
    at /usr/src/debug/kdepim-4.3.1/x86_64-redhat-linux-gnu/libkdepim/ldapclient.moc:92
#18 0x000000302bb58f52 in QMetaObject::activate () from /usr/lib64/libQtCore.so.4
#19 0x00007f23d269de52 in KJob::result (this=0x7fffd9bef840, _t1=0x34e5740) at /usr/src/debug/kdelibs-4.3.1/x86_64-redhat-linux-gnu/kdecore/kjob.moc:188
#20 0x00007f23d269e1cf in KJob::emitResult (this=0x34e5740) at /usr/src/debug/kdelibs-4.3.1/kdecore/jobs/kjob.cpp:304
#21 0x00007f23d3130080 in KIO::SimpleJob::slotFinished (this=0x34e5740) at /usr/src/debug/kdelibs-4.3.1/kio/kio/job.cpp:477
#22 0x00007f23d3130533 in KIO::TransferJob::slotFinished (this=0x34e5740) at /usr/src/debug/kdelibs-4.3.1/kio/kio/job.cpp:948
#23 0x00007f23d312b325 in KIO::TransferJob::qt_metacall (this=0x34e5740, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fffd9bf00b0)
    at /usr/src/debug/kdelibs-4.3.1/x86_64-redhat-linux-gnu/kio/jobclasses.moc:343
#24 0x000000302bb58f52 in QMetaObject::activate () from /usr/lib64/libQtCore.so.4
#25 0x00007f23d31ede61 in KIO::SlaveInterface::dispatch (this=0x20df390, _cmd=104, rawdata=<value optimized out>) at /usr/src/debug/kdelibs-4.3.1/kio/kio/slaveinterface.cpp:175
#26 0x00007f23d31ea9b2 in KIO::SlaveInterface::dispatch (this=0x20df390) at /usr/src/debug/kdelibs-4.3.1/kio/kio/slaveinterface.cpp:91
#27 0x00007f23d31dd533 in KIO::Slave::gotInput (this=0x20df390) at /usr/src/debug/kdelibs-4.3.1/kio/kio/slave.cpp:322
#28 0x00007f23d31df798 in KIO::Slave::qt_metacall (this=0x20df390, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7fffd9bf04d0) at /usr/src/debug/kdelibs-4.3.1/x86_64-redhat-linux-gnu/kio/slave.moc:76
#29 0x000000302bb58f52 in QMetaObject::activate () from /usr/lib64/libQtCore.so.4
#30 0x00007f23d30f8c21 in KIO::ConnectionPrivate::dequeue (this=0x21f70d0) at /usr/src/debug/kdelibs-4.3.1/kio/kio/connection.cpp:82
#31 0x00007f23d30f907a in KIO::Connection::qt_metacall (this=0x3063790, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x3aca910)
    at /usr/src/debug/kdelibs-4.3.1/x86_64-redhat-linux-gnu/kio/connection.moc:73
#32 0x000000302bb540d8 in QObject::event () from /usr/lib64/libQtCore.so.4
#33 0x000000302d39008d in QApplicationPrivate::notify_helper () from /usr/lib64/libQtGui.so.4
#34 0x000000302d3982ca in QApplication::notify () from /usr/lib64/libQtGui.so.4
#35 0x00007f23d2c404ab in KApplication::notify (this=0x7fffd9bf0f30, receiver=0x3063790, event=0x34b22b0) at /usr/src/debug/kdelibs-4.3.1/kdeui/kernel/kapplication.cpp:302
#36 0x000000302bb4407c in QCoreApplication::notifyInternal () from /usr/lib64/libQtCore.so.4
#37 0x000000302bb44cea in QCoreApplicationPrivate::sendPostedEvents () from /usr/lib64/libQtCore.so.4
#38 0x000000302bb6d903 in ?? () from /usr/lib64/libQtCore.so.4
#39 0x0000003bcd8377bb in g_main_context_dispatch () from /lib64/libglib-2.0.so.0
#40 0x0000003bcd83af8d in ?? () from /lib64/libglib-2.0.so.0
#41 0x0000003bcd83b14b in g_main_context_iteration () from /lib64/libglib-2.0.so.0
#42 0x000000302bb6d58f in QEventDispatcherGlib::processEvents () from /usr/lib64/libQtCore.so.4
#43 0x000000302d4274cf in ?? () from /usr/lib64/libQtGui.so.4
#44 0x000000302bb42912 in QEventLoop::processEvents () from /usr/lib64/libQtCore.so.4
#45 0x000000302bb42ce4 in QEventLoop::exec () from /usr/lib64/libQtCore.so.4
#46 0x000000302bb44fb4 in QCoreApplication::exec () from /usr/lib64/libQtCore.so.4
#47 0x00000000004045f5 in main (argc=1, argv=0x7fffd9bf1618) at /usr/src/debug/kdepim-4.3.1/kontact/src/main.cpp:218

Reported using DrKonqi