Oh, some more info:

Before it crashed, there were three apps listed after the 3rd typed-in letter and after the 4th letter, the 2nd entry got empty (remaining apps on the 1st and the 3rd position), krunner froze and then crashed after 2 seconds.

This could be related to bug 218950 and its related ones.
- Which KDE SC and Qt versions (SVN and git revisions) are you using ?
Bug 218950 is related to Qt4.6.0 (a bug already fixed in 4.6.1 and kde-qt)
If you are not sure, may be we can confirm this with a full backtrace
Regards

Yes, it's Qt 4.6.0 here. Can you tell me how to produce a full backtrace? Is it the one DrKonqui creates?

- Which GNU/Linux distribution or system are you using ?

Debian GNU/Linux Sid (Unstable)

- What is your Qt4 version ?
To get a full backtrace you need to install the "libqt4-dbg" package and fetch it using DrKonqi or GDB. 
Thanks

As stated in Comment #3, my Qt version is 4.6.0. I thought I had Qt's debugging symbols installed (I always had) but the package was missing. So here is the new backtrace with the package installed:

GDB:
Program received signal SIGSEGV, Segmentation fault.
0xb5140bc1 in malloc_consolidate (av=0xb52193c0) at malloc.c:5125
5125    malloc.c: No such file or directory.
        in malloc.c
Current language:  auto
The current source language is "auto; currently c".
(gdb) bt
#0  0xb5140bc1 in malloc_consolidate (av=0xb52193c0) at malloc.c:5125
#1  0xb5142d86 in _int_malloc (av=0xb52193c0, bytes=534) at malloc.c:4360
#2  0xb5143f78 in malloc_check (sz=533, caller=0xb5557e1d) at hooks.c:264
#3  0xb5145308 in *__GI___libc_malloc (bytes=533) at malloc.c:3622
#4  0xb5557e1d in qMalloc (size=533) at global/qmalloc.cpp:55
#5  0xb5560d1b in QByteArray::resize (this=0xbfffeff4, size=513) at tools/qbytearray.cpp:1359
#6  0xb5c60985 in QKeyMapperPrivate::translateKeyEventInternal (this=0x80a0720, keyWidget=0x8149d80, event=0xbffff3c8, keysym=@0xbffff2e0, count=@0xbffff2f0, text=..., modifiers=..., code=@0xbffff2f4, type=@0xbff
ff2e8, statefulTranslation=false) at kernel/qkeymapper_x11.cpp:1541
#7  0xb5c3633e in QApplication::x11ProcessEvent (this=0x806c268, event=0xbffff3c8) at kernel/qapplication_x11.cpp:3215
#8  0xb5c6491f in QEventDispatcherX11::processEvents (this=0x806b4c8, flags=...) at kernel/qeventdispatcher_x11.cpp:132
#9  0xb565ea3a in QEventLoop::processEvents (this=0xbffff4e0, flags=...) at kernel/qeventloop.cpp:149
#10 0xb565ee82 in QEventLoop::exec (this=0xbffff4e0, flags=...) at kernel/qeventloop.cpp:201
#11 0xb5661599 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:981
#12 0xb5ba7bf7 in QApplication::exec () at kernel/qapplication.cpp:3570
#13 0xb7fb0bae in kdemain (argc=2, argv=0xbffff674) at /home/fs/kdesvn/kdebase/workspace/krunner/main.cpp:65
#14 0x0804879b in main (argc=2, argv=0xbffff674) at /home/fs/kdesvn/build/kdebase/workspace/krunner/krunner_dummy.cpp:3


DrKonqui:
Application: Oberfläche zur Ausführung von Befehlen (kdeinit4), signal: Segmentation fault
[Current thread is 1 (Thread 0xb55dd760 (LWP 2894))]

Thread 6 (Thread 0xa868bb70 (LWP 2903)):
#0  0xffffe424 in __kernel_vsyscall ()
#1  0xb69930a5 in pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
#2  0xb6a12602 in QWaitConditionPrivate::wait (this=0xa1c7aa0, mutex=0xa1c7a9c, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#3  QWaitCondition::wait (this=0xa1c7aa0, mutex=0xa1c7a9c, time=4294967295) at thread/qwaitcondition_unix.cpp:159
#4  0xb7121a9a in QHostInfoAgent::run (this=0xa1c7a90) at kernel/qhostinfo.cpp:252
#5  0xb6a1170e in QThreadPrivate::start (arg=0xa1c7a90) at thread/qthread_unix.cpp:244
#6  0xb698f585 in start_thread (arg=0xa868bb70) at pthread_create.c:300
#7  0xb5cfa2be in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 5 (Thread 0xa7e57b70 (LWP 3013)):
#0  0xffffe424 in __kernel_vsyscall ()
#1  0xb69930a5 in pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
#2  0xb6a12602 in QWaitConditionPrivate::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#3  QWaitCondition::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:159
#4  0xb40d18c0 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0x9f911a0, th=0xa1fd8a0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb40d438c in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0x9f8ed20, th=0xa1fd8a0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb40d028b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0x9f911a0, th=0xa1fd8a0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb40d4482 in ThreadWeaver::WorkingHardState::applyForWork (this=0x9f8ed20, th=0xa1fd8a0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb40d1b43 in ThreadWeaver::WeaverImpl::applyForWork (this=0x9f911a0, th=0xa1fd8a0, previous=0xa7208a8) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb40d251e in ThreadWeaver::ThreadRunHelper::run (this=0xa7e572c4, parent=0x9f911a0, th=0xa1fd8a0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:87
#10 0xb40d2c3b in ThreadWeaver::Thread::run (this=0xa1fd8a0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:142
#11 0xb6a1170e in QThreadPrivate::start (arg=0xa1fd8a0) at thread/qthread_unix.cpp:244
#12 0xb698f585 in start_thread (arg=0xa7e57b70) at pthread_create.c:300
#13 0xb5cfa2be in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 4 (Thread 0xa7656b70 (LWP 3014)):
#0  0xffffe424 in __kernel_vsyscall ()
#1  0xb69930a5 in pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
#2  0xb6a12602 in QWaitConditionPrivate::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#3  QWaitCondition::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:159
#4  0xb40d18c0 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0x9f911a0, th=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb40d438c in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0x9f8ed20, th=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb40d028b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0x9f911a0, th=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb40d4482 in ThreadWeaver::WorkingHardState::applyForWork (this=0x9f8ed20, th=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb40d1b43 in ThreadWeaver::WeaverImpl::applyForWork (this=0x9f911a0, th=0xa20de88, previous=0x0) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb40d44a1 in ThreadWeaver::WorkingHardState::applyForWork (this=0x9f8ed20, th=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:74
#10 0xb40d1b43 in ThreadWeaver::WeaverImpl::applyForWork (this=0x9f911a0, th=0xa20de88, previous=0xa720c38) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:351
#11 0xb40d251e in ThreadWeaver::ThreadRunHelper::run (this=0xa76562c4, parent=0x9f911a0, th=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:87
#12 0xb40d2c3b in ThreadWeaver::Thread::run (this=0xa20de88) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:142
#13 0xb6a1170e in QThreadPrivate::start (arg=0xa20de88) at thread/qthread_unix.cpp:244
#14 0xb698f585 in start_thread (arg=0xa7656b70) at pthread_create.c:300
#15 0xb5cfa2be in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 3 (Thread 0xa6e55b70 (LWP 3015)):
#0  0xffffe424 in __kernel_vsyscall ()
#1  0xb69930a5 in pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
#2  0xb6a12602 in QWaitConditionPrivate::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#3  QWaitCondition::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:159
#4  0xb40d18c0 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0x9f911a0, th=0xa205290) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb40d438c in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0x9f8ed20, th=0xa205290) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb40d028b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0x9f911a0, th=0xa205290) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb40d4482 in ThreadWeaver::WorkingHardState::applyForWork (this=0x9f8ed20, th=0xa205290) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb40d1b43 in ThreadWeaver::WeaverImpl::applyForWork (this=0x9f911a0, th=0xa205290, previous=0xa759748) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb40d251e in ThreadWeaver::ThreadRunHelper::run (this=0xa6e552c4, parent=0x9f911a0, th=0xa205290) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:87
#10 0xb40d2c3b in ThreadWeaver::Thread::run (this=0xa205290) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:142
#11 0xb6a1170e in QThreadPrivate::start (arg=0xa205290) at thread/qthread_unix.cpp:244
#12 0xb698f585 in start_thread (arg=0xa6e55b70) at pthread_create.c:300
#13 0xb5cfa2be in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 2 (Thread 0xa6654b70 (LWP 3016)):
#0  0xffffe424 in __kernel_vsyscall ()
#1  0xb69930a5 in pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
#2  0xb6a12602 in QWaitConditionPrivate::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#3  QWaitCondition::wait (this=0x9f911b8, mutex=0x9f914a0, time=4294967295) at thread/qwaitcondition_unix.cpp:159
#4  0xb40d18c0 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0x9f911a0, th=0xa219958) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb40d438c in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0x9f8ed20, th=0xa219958) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb40d028b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0x9f911a0, th=0xa219958) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb40d4482 in ThreadWeaver::WorkingHardState::applyForWork (this=0x9f8ed20, th=0xa219958) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb40d1b43 in ThreadWeaver::WeaverImpl::applyForWork (this=0x9f911a0, th=0xa219958, previous=0xa14a338) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb40d251e in ThreadWeaver::ThreadRunHelper::run (this=0xa66542c4, parent=0x9f911a0, th=0xa219958) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:87
#10 0xb40d2c3b in ThreadWeaver::Thread::run (this=0xa219958) at /home/fs/kdesvn/kdelibs/threadweaver/Weaver/Thread.cpp:142
#11 0xb6a1170e in QThreadPrivate::start (arg=0xa219958) at thread/qthread_unix.cpp:244
#12 0xb698f585 in start_thread (arg=0xa6654b70) at pthread_create.c:300
#13 0xb5cfa2be in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 1 (Thread 0xb55dd760 (LWP 2894)):
[KCrash Handler]
#6  QGraphicsScenePrivate::processDirtyItemsRecursive (this=0xa021028, item=0xa251668, dirtyAncestorContainsChildren=false, parentOpacity=1) at graphicsview/qgraphicsscene.cpp:4895
#7  0xb669c460 in QGraphicsScenePrivate::_q_processDirtyItems (this=0xa021028) at graphicsview/qgraphicsscene.cpp:466
#8  0xb669c9de in QGraphicsScene::qt_metacall (this=0xa03a4a8, _c=QMetaObject::InvokeMetaMethod, _id=14, _a=0xa14bf08) at .moc/release-shared/moc_qgraphicsscene.cpp:130
#9  0xb3ac3aba in ResultScene::qt_metacall (this=0xa03a4a8, _c=QMetaObject::InvokeMetaMethod, _id=18, _a=0xa14bf08) at /home/fs/kdesvn/build/kdebase/workspace/krunner/resultscene.moc:93
#10 0xb6b19755 in QMetaObject::metacall (object=0xa251668, cl=QMetaObject::InvokeMetaMethod, idx=18, argv=0xa14bf08) at kernel/qmetaobject.cpp:237
#11 0xb6b23cc6 in QMetaCallEvent::placeMetaCall (this=0xa7886f0, object=0xa03a4a8) at kernel/qobject.cpp:574
#12 0xb6b25163 in QObject::event (this=0xa03a4a8, e=0xa7886f0) at kernel/qobject.cpp:1260
#13 0xb669798e in QGraphicsScene::event (this=0xa03a4a8, event=0xa7886f0) at graphicsview/qgraphicsscene.cpp:3450
#14 0xb5fffb5c in QApplicationPrivate::notify_helper (this=0x9eef5c8, receiver=0xa03a4a8, e=0xa7886f0) at kernel/qapplication.cpp:4242
#15 0xb600733d in QApplication::notify (this=0x9eef3d0, receiver=0xa03a4a8, e=0xa7886f0) at kernel/qapplication.cpp:3661
#16 0xb6e853ea in KApplication::notify (this=0x9eef3d0, receiver=0xa03a4a8, event=0xa7886f0) at /home/fs/kdesvn/kdelibs/kdeui/kernel/kapplication.cpp:302
#17 0xb6b143eb in QCoreApplication::notifyInternal (this=0x9eef3d0, receiver=0xa03a4a8, event=0xa7886f0) at kernel/qcoreapplication.cpp:704
#18 0xb6b1531f in QCoreApplication::sendEvent (receiver=0x0, event_type=0, data=0x9e9daf8) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#19 QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x9e9daf8) at kernel/qcoreapplication.cpp:1345
#20 0xb6b154cd in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1238
#21 0xb60bc73e in QCoreApplication::sendPostedEvents (this=0x9eef5a8, flags=...) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:220
#22 QEventDispatcherX11::processEvents (this=0x9eef5a8, flags=...) at kernel/qeventdispatcher_x11.cpp:75
#23 0xb6b12a3a in QEventLoop::processEvents (this=0xbf9637c0, flags=...) at kernel/qeventloop.cpp:149
#24 0xb6b12e82 in QEventLoop::exec (this=0xbf9637c0, flags=...) at kernel/qeventloop.cpp:201
#25 0xb6b15599 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:981
#26 0xb5fffbf7 in QApplication::exec () at kernel/qapplication.cpp:3570
#27 0xb3ab7bae in kdemain (argc=1, argv=0x9ee1160) at /home/fs/kdesvn/kdebase/workspace/krunner/main.cpp:65
#28 0x0804e0c9 in launch (argc=<value optimized out>, _name=<value optimized out>, args=<value optimized out>, cwd=0x0, envc=0, envs=0x9ee08d1 "", reset_env=false, tty=0x0, avoid_loops=false, 
    startup_id_str=0x805120b "0") at /home/fs/kdesvn/kdelibs/kinit/kinit.cpp:705
#29 0x0804ebfd in handle_launcher_request (sock=<value optimized out>, who=<value optimized out>) at /home/fs/kdesvn/kdelibs/kinit/kinit.cpp:1197
#30 0x0804f094 in handle_requests (waitForPid=<value optimized out>) at /home/fs/kdesvn/kdelibs/kinit/kinit.cpp:1390
#31 0x0804f93f in main (argc=4, argv=0xbf964294, envp=0xbf9642a8) at /home/fs/kdesvn/kdelibs/kinit/kinit.cpp:1825

This is bug 210146 (and its krunner duplicates): the Qt4.6.0 bug, fixed in 4.6.1 and kde-qt
Thanks

*** This bug has been marked as a duplicate of bug 210146 ***

Thanks. :)

*** This bug has been marked as a duplicate of bug 210146 ***