If you can reproduce the crash at will, may you read http://techbase.kde.org/Development/Tutorials/Debugging/How_to_create_useful_crash_reports and post a complete backtrace here? Thanks

I have the same problem. I downloaded the debug package, read the how to on creating a bug report, and saved the backtrace.  Then I rebooted to see if it would happen again and it did.  I have one alarm set for about a half hour from the current time. It's set as a text message alarm with no sound for today's date. I had no other programs running when I duplicated the crash after rebooting. When I try to close the program with the window "X" nothing happens. Then I click quit in the drop down menu and it warns me that alarms will be disabled.  I clicked quit on the warning message and the crash handler shows up with: 
A Fatal Error Occurred
The application KAlarm (kalarm) crashed and caused the signal 11 (SIGSEGV).

Here is the backtrace:

Application: KAlarm (kalarm), signal SIGSEGV

Thread 1 (Thread 0xb4fe4700 (LWP 3542)):
[KCrash Handler]
#6  QSortFilterProxyModelPrivate::proxy_to_source (this=0x8802070, proxy_index=@0xbfe98388) at ../../include/QtCore/../../src/corelib/tools/qvector.h:117
#7  0xb713aa93 in QSortFilterProxyModel::mapToSource (this=0x881cb28, proxyIndex=@0xbfe98388) at itemviews/qsortfilterproxymodel.cpp:2346
#8  0xb713a3d2 in QSortFilterProxyModel::data (this=0x881cb28, index=@0xbfe98388, role=0) at itemviews/qsortfilterproxymodel.cpp:1573
#9  0x08157596 in AlarmListDelegate::sizeHint (this=0x8867b40, option=@0xbfe982e8, index=@0xbfe98388) at /usr/include/qt4/QtCore/qabstractitemmodel.h:378
#10 0xb70f4026 in QTreeView::sizeHintForColumn (this=0x88162a8, column=0) at itemviews/qtreeview.cpp:2709
#11 0xb70bcc12 in QHeaderViewPrivate::viewSectionSizeHint (this=0x8886fe0, logical=0) at itemviews/qheaderview.cpp:3456
#12 0xb70c41a3 in QHeaderViewPrivate::resizeSections (this=0x8886fe0, globalMode=QHeaderView::Interactive, useGlobalMode=false) at itemviews/qheaderview.cpp:2985
#13 0xb70c47c7 in QHeaderView::resizeSections (this=0x8859ec0) at itemviews/qheaderview.cpp:1613
#14 0xb70c52df in QHeaderView::viewportEvent (this=0x8859ec0, e=0xbfe988dc) at itemviews/qheaderview.cpp:2391
#15 0xb700af55 in QAbstractScrollAreaFilter::eventFilter (this=0x8801f70, o=0x881cae0, e=0xbfe988dc) at widgets/qabstractscrollarea_p.h:100
#16 0xb6664c5a in QCoreApplicationPrivate::sendThroughObjectEventFilters (this=0x862f108, receiver=0x881cae0, event=0xbfe988dc) at kernel/qcoreapplication.cpp:718
#17 0xb6b37e7a in QApplicationPrivate::notify_helper (this=0x862f108, receiver=0x881cae0, e=0xbfe988dc) at kernel/qapplication.cpp:4080
#18 0xb6b40282 in QApplication::notify (this=0x862beb0, receiver=0x881cae0, e=0xbfe988dc) at kernel/qapplication.cpp:4049
#19 0xb775b94d in KApplication::notify (this=0x862beb0, receiver=0x881cae0, event=0xbfe988dc) at /build/buildd/kde4libs-4.2.2/kdeui/kernel/kapplication.cpp:307
#20 0xb6665a3b in QCoreApplication::notifyInternal (this=0x862beb0, receiver=0x881cae0, event=0xbfe988dc) at kernel/qcoreapplication.cpp:602
#21 0xb6b8cdc6 in QWidgetPrivate::hideChildren (this=0x8886fe0, spontaneous=false) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#22 0xb6b8cd00 in QWidgetPrivate::hideChildren (this=0x88865b8, spontaneous=false) at kernel/qwidget.cpp:7045
#23 0xb6b8cd00 in QWidgetPrivate::hideChildren (this=0x88211a0, spontaneous=false) at kernel/qwidget.cpp:7045
#24 0xb6b8cd00 in QWidgetPrivate::hideChildren (this=0x8823c48, spontaneous=false) at kernel/qwidget.cpp:7045
#25 0xb6b8cf08 in QWidgetPrivate::hide_helper (this=0x8823c48) at kernel/qwidget.cpp:6809
#26 0xb6b94920 in QWidget::setVisible (this=0x8617038, visible=false) at kernel/qwidget.cpp:6978
#27 0xb6b8989d in ~QWidget (this=0x8617038) at ../../include/QtGui/../../src/gui/kernel/qwidget.h:477
#28 0xb6f85531 in ~QMainWindow (this=0x8617038) at widgets/qmainwindow.cpp:328
#29 0xb784013b in ~KMainWindow (this=0x8617038) at /build/buildd/kde4libs-4.2.2/kdeui/widgets/kmainwindow.cpp:467
#30 0xb7883267 in ~KXmlGuiWindow (this=0x8617038, __vtt_parm=0x81a0180) at /build/buildd/kde4libs-4.2.2/kdeui/xmlgui/kxmlguiwindow.cpp:127
#31 0x080ecb54 in ~MainWindow (this=0x8617038) at /build/buildd/kdepim-4.2.2/obj-i486-linux-gnu/kalarm/../../kalarm/mainwindowbase.h:37
#32 0x080eb075 in MainWindow::closeAll () at /build/buildd/kdepim-4.2.2/kalarm/mainwindow.cpp:286
#33 0x080db321 in KAlarmApp::quitIf (this=0x862beb0, exitCode=0, force=true) at /build/buildd/kdepim-4.2.2/kalarm/kalarmapp.cpp:767
#34 0x080db97b in KAlarmApp::doQuit (this=0x862beb0, parent=0x8617038) at /build/buildd/kdepim-4.2.2/kalarm/kalarmapp.cpp:821
#35 0x080ea8da in MainWindow::slotQuit (this=0x8617038) at /build/buildd/kdepim-4.2.2/kalarm/mainwindow.cpp:1083
#36 0x080f5255 in MainWindow::qt_metacall (this=0x8617038, _c=QMetaObject::InvokeMetaMethod, _id=22, _a=0x8a6f9b8) at /build/buildd/kdepim-4.2.2/obj-i486-linux-gnu/kalarm/mainwindow.moc:153
#37 0xb66748fb in QMetaCallEvent::placeMetaCall (this=0x8ab3270, object=0x8617038) at kernel/qobject.cpp:489
#38 0xb66763a0 in QObject::event (this=0x8617038, e=0x8ab3270) at kernel/qobject.cpp:1118
#39 0xb6b8e440 in QWidget::event (this=0x8617038, event=0x8ab3270) at kernel/qwidget.cpp:7913
#40 0xb6f860d7 in QMainWindow::event (this=0x8617038, event=0x8ab3270) at widgets/qmainwindow.cpp:1396
#41 0xb783f327 in KMainWindow::event (this=0x8617038, ev=0x8ab3270) at /build/buildd/kde4libs-4.2.2/kdeui/widgets/kmainwindow.cpp:1094
#42 0xb788410c in KXmlGuiWindow::event (this=0x8617038, ev=0x8ab3270) at /build/buildd/kde4libs-4.2.2/kdeui/xmlgui/kxmlguiwindow.cpp:131
#43 0xb6b37e9c in QApplicationPrivate::notify_helper (this=0x862f108, receiver=0x8617038, e=0x8ab3270) at kernel/qapplication.cpp:4084
#44 0xb6b40282 in QApplication::notify (this=0x862beb0, receiver=0x8617038, e=0x8ab3270) at kernel/qapplication.cpp:4049
#45 0xb775b94d in KApplication::notify (this=0x862beb0, receiver=0x8617038, event=0x8ab3270) at /build/buildd/kde4libs-4.2.2/kdeui/kernel/kapplication.cpp:307
#46 0xb6665a3b in QCoreApplication::notifyInternal (this=0x862beb0, receiver=0x8617038, event=0x8ab3270) at kernel/qcoreapplication.cpp:602
#47 0xb6666695 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x85f8df0) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#48 0xb666688d in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1132
#49 0xb66917ef in postEventSourceDispatch (s=0x8631310) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#50 0xb5599b88 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#51 0xb559d0eb in ?? () from /usr/lib/libglib-2.0.so.0
#52 0xb559d268 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#53 0xb6691438 in QEventDispatcherGlib::processEvents (this=0x85fd468, flags={i = -1075211208}) at kernel/qeventdispatcher_glib.cpp:323
#54 0xb6bd9365 in QGuiEventDispatcherGlib::processEvents (this=0x85fd468, flags={i = -1075211160}) at kernel/qguieventdispatcher_glib.cpp:202
#55 0xb666406a in QEventLoop::processEvents (this=0xbfe994e0, flags={i = -1075211096}) at kernel/qeventloop.cpp:149
#56 0xb66644aa in QEventLoop::exec (this=0xbfe994e0, flags={i = -1075211032}) at kernel/qeventloop.cpp:200
#57 0xb6666959 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:880
#58 0xb6b37d17 in QApplication::exec () at kernel/qapplication.cpp:3553
#59 0x08096b2e in main (argc=5, argv=0xbfe99944) at /build/buildd/kdepim-4.2.2/kalarm/main.cpp:123

Fixed in KDE 4.2.3.

*** This bug has been marked as a duplicate of bug 189929 ***

I don't have details. I started my Fedora 11 (64bits) and I received this:
The application KAlarm (kalarm) crashed and caused the signal 11 (SIGSEGV).
Please help us improve the software you use by filing a report at http://bugs.kde.org. Useful details include how to reproduce the error, documents that were loaded, etc.
I think it is because I didn't close the program before shut down the system.