Steps:

- Select a folder
- type S
- enter a word
- Click on the search button

Always reproducible

kmail2(12900) KMail::SearchWindow::searchDone: "Unable to create persistent search" 
ASSERT: "mFolder.isValid()" in file /kde/src/KDE/kdepim/kmail/searchwindow.cpp, line 523

Program received signal SIGABRT, Aborted.
0x00007ffff52a9ab5 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff52a9ab5 in raise () from /lib64/libc.so.6
#1  0x00007ffff52aafb6 in abort () from /lib64/libc.so.6
#2  0x00007ffff6812924 in qt_message_output (msgType=<optimized out>, buf=<optimized out>) at global/qglobal.cpp:2282
#3  0x00007ffff6812aed in qt_message(QtMsgType, const char *, typedef __va_list_tag __va_list_tag *) (msgType=QtFatalMsg, msg=0x7ffff6964ba8 "ASSERT: \"%s\" in file %s, line %d", ap=0x7fffffffa420) at global/qglobal.cpp:2328
#4  0x00007ffff6812c85 in qFatal (msg=<optimized out>) at global/qglobal.cpp:2511
#5  0x00007ffff6812cca in qt_assert (assertion=0x3264 <Address 0x3264 out of bounds>, file=0x6 <Address 0x6 out of bounds>, line=-1) at global/qglobal.cpp:2027
#6  0x00007ffff6d4774e in KMail::SearchWindow::searchDone (this=0xfc1340, job=0x10b60c0) at /kde/src/KDE/kdepim/kmail/searchwindow.cpp:523
#7  0x00007ffff6d499c4 in KMail::SearchWindow::qt_metacall(enum QMetaObject::Call, int, void **) (this=0xfc1340, _c=QMetaObject::InvokeMetaMethod, _id=23, _a=0x7fffffffa6f0) at /kde/build/KDE/kdepim/kmail/searchwindow.moc:143
#8  0x00007ffff6919a5f in QMetaObject::activate (sender=0x10b60c0, m=<optimized out>, local_signal_index=<optimized out>, argv=0x7fffffffa6f0) at kernel/qobject.cpp:3278
#9  0x00007ffff73f5ce2 in KJob::result (this=<optimized out>, _t1=0x10b60c0) at /usr/src/debug/kdelibs-4.6.41_20110406/build/kdecore/kjob.moc:194
#10 0x00007ffff73f5d20 in KJob::emitResult (this=0x10b60c0) at /usr/src/debug/kdelibs-4.6.41_20110406/kdecore/jobs/kjob.cpp:312
#11 0x00007ffff180d540 in Akonadi::JobPrivate::handleResponse (this=0x10be030, tag="48" = {...}, data="NO Unable to create persistent search\r\n" = {...}) at /kde/src/KDE/kdepimlibs/akonadi/job.cpp:66
#12 0x00007ffff184a99d in Akonadi::SessionPrivate::dataReceived (this=0x9397b0) at /kde/src/KDE/kdepimlibs/akonadi/session.cpp:218
#13 0x00007ffff184c16e in Akonadi::Session::qt_metacall (this=0x938ec0, _c=QMetaObject::InvokeMetaMethod, _id=5, _a=0x7fffffffa9f0) at /kde/build/KDE/kdepimlibs/akonadi/session.moc:96
#14 0x00007ffff6919a5f in QMetaObject::activate (sender=0x811a80, m=<optimized out>, local_signal_index=<optimized out>, argv=0x0) at kernel/qobject.cpp:3278
#15 0x00007ffff6960d98 in QIODevice::qt_metacall (this=0x811a80, _c=QMetaObject::InvokeMetaMethod, _id=<optimized out>, _a=0x7fffffffab10) at .moc/release-shared/moc_qiodevice.cpp:77
#16 0x00007ffff4398ca0 in QLocalSocket::qt_metacall (this=0x811a80, _c=QMetaObject::InvokeMetaMethod, _id=<optimized out>, _a=0x7fffffffab10) at .moc/release-shared/moc_qlocalsocket.cpp:81
#17 0x00007ffff6919a5f in QMetaObject::activate (sender=0x960100, m=<optimized out>, local_signal_index=<optimized out>, argv=0x0) at kernel/qobject.cpp:3278
#18 0x00007ffff43946df in QAbstractSocketPrivate::canReadNotification (this=0x942510) at socket/qabstractsocket.cpp:639
#19 0x00007ffff43822e1 in QReadNotifier::event (this=<optimized out>, e=<optimized out>) at socket/qnativesocketengine.cpp:1103
#20 0x00007ffff5ccd144 in QApplicationPrivate::notify_helper (this=0x65e330, receiver=0x9629f0, e=0x7fffffffb0b0) at kernel/qapplication.cpp:4462
#21 0x00007ffff5cd56fa in QApplication::notify (this=<optimized out>, receiver=0x9629f0, e=0x7fffffffb0b0) at kernel/qapplication.cpp:4341
#22 0x00007ffff79c2a76 in KApplication::notify (this=0x7fffffffb670, receiver=0x9629f0, event=0x7fffffffb0b0) at /usr/src/debug/kdelibs-4.6.41_20110406/kdeui/kernel/kapplication.cpp:311
#23 0x00007ffff690547c in QCoreApplication::notifyInternal (this=0x7fffffffb670, receiver=0x9629f0, event=0x7fffffffb0b0) at kernel/qcoreapplication.cpp:731
#24 0x00007ffff69314db in sendEvent (event=0x7fffffffb0b0, receiver=<optimized out>) at kernel/qcoreapplication.h:215
#25 QEventDispatcherUNIX::activateSocketNotifiers (this=<optimized out>) at kernel/qeventdispatcher_unix.cpp:892
#26 0x00007ffff69323d6 in QEventDispatcherUNIXPrivate::doSelect (this=<optimized out>, flags=Cannot access memory at address 0x7fff00000000
) at kernel/qeventdispatcher_unix.cpp:305
#27 0x00007ffff69334ef in QEventDispatcherUNIX::processEvents (this=0x6117c0, flags=...) at kernel/qeventdispatcher_unix.cpp:934
#28 0x00007ffff5d739cc in QEventDispatcherX11::processEvents (this=0x6117c0, flags=...) at kernel/qeventdispatcher_x11.cpp:152
#29 0x00007ffff69048d2 in QEventLoop::processEvents (this=<optimized out>, flags=...) at kernel/qeventloop.cpp:149
#30 0x00007ffff6904ae5 in QEventLoop::exec (this=0x7fffffffb530, flags=...) at kernel/qeventloop.cpp:201
#31 0x00007ffff6908f2b in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1008
#32 0x0000000000403474 in main (argc=2, argv=0x7fffffffb808) at /kde/src/KDE/kdepim/kmail/main.cpp:145