When I create a subfolder to the 'inbox' folder, when I try to move mail there or from there, I get various error messages like:

>Lokale Ordner: Das Maildir „/home/xaverw/.local/share/local-mail/.Posteingang.directory/Versand“ für die Sammlung „Versand“ ist ungültig.

>Lokale Ordner: Der Zielordner ist ungültig: „Error opening /home/xaverw/.local/share/local-mail/.Posteingang.directory/Versand; this folder is missing.“

>Lokale Ordner: Der Unterordner „Personal“ kann nicht gelöscht werden.

(If it helps I can try to provide free translations).

Sometimes, this is accompanied by a crash of Kontact. I can't really test the reproducibility as I can't jeopardize my mail, but these problems and crashes have repeated. The last backtrace I got from KCrash was:

Application: Kontact (kontact), signal: Segmentation fault
Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".
[Current thread is 1 (Thread 0xb76e3980 (LWP 3542))]

Thread 4 (Thread 0xb5658b40 (LWP 3543)):
#0  0x006b5416 in __kernel_vsyscall ()
#1  0x00a5596b in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/i386-linux-gnu/libpthread.so.0
#2  0x052713dc in pthread_cond_wait () from /lib/i386-linux-gnu/libc.so.6
#3  0x06782263 in ?? () from /usr/lib/i386-linux-gnu/libQtWebKit.so.4
#4  0x0678237f in ?? () from /usr/lib/i386-linux-gnu/libQtWebKit.so.4
#5  0x00a51d4c in start_thread () from /lib/i386-linux-gnu/libpthread.so.0
#6  0x05263ace in clone () from /lib/i386-linux-gnu/libc.so.6

Thread 3 (Thread 0xb4d2fb40 (LWP 3544)):
#0  0x009fbdcd in clock_gettime () from /lib/i386-linux-gnu/librt.so.1
#1  0x088c8315 in do_gettime (frac=0xb4d2f040, sec=0xb4d2f038) at tools/qelapsedtimer_unix.cpp:123
#2  qt_gettime () at tools/qelapsedtimer_unix.cpp:140
#3  0x089b2226 in QTimerInfoList::updateCurrentTime (this=0xb4402074) at kernel/qeventdispatcher_unix.cpp:343
#4  0x089b1e16 in timerSourceCheckHelper (src=0xb4402040) at kernel/qeventdispatcher_glib.cpp:150
#5  timerSourceCheckHelper (src=0xb4402040) at kernel/qeventdispatcher_glib.cpp:144
#6  0x019e6b7b in g_main_context_check () from /lib/i386-linux-gnu/libglib-2.0.so.0
#7  0x019e7042 in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#8  0x019e7201 in g_main_context_iteration () from /lib/i386-linux-gnu/libglib-2.0.so.0
#9  0x089b18e7 in QEventDispatcherGlib::processEvents (this=0xb4400468, flags=...) at kernel/qeventdispatcher_glib.cpp:426
#10 0x0897d50d in QEventLoop::processEvents (this=0xb4d2f270, flags=...) at kernel/qeventloop.cpp:149
#11 0x0897d7a9 in QEventLoop::exec (this=0xb4d2f270, flags=...) at kernel/qeventloop.cpp:204
#12 0x0886694c in QThread::exec (this=0x9bdb400) at thread/qthread.cpp:501
#13 0x08866a3b in QThread::run (this=0x9bdb400) at thread/qthread.cpp:568
#14 0x08869de0 in QThreadPrivate::start (arg=0x9bdb400) at thread/qthread_unix.cpp:298
#15 0x00a51d4c in start_thread () from /lib/i386-linux-gnu/libpthread.so.0
#16 0x05263ace in clone () from /lib/i386-linux-gnu/libc.so.6

Thread 2 (Thread 0xb2a9fb40 (LWP 3560)):
#0  0x009fbdcd in clock_gettime () from /lib/i386-linux-gnu/librt.so.1
#1  0x088c8315 in do_gettime (frac=0xb2a9efb0, sec=0xb2a9efa8) at tools/qelapsedtimer_unix.cpp:123
#2  qt_gettime () at tools/qelapsedtimer_unix.cpp:140
#3  0x089b2226 in QTimerInfoList::updateCurrentTime (this=0xb2102074) at kernel/qeventdispatcher_unix.cpp:343
#4  0x089b257a in QTimerInfoList::timerWait (this=0xb2102074, tm=...) at kernel/qeventdispatcher_unix.cpp:450
#5  0x089b0e23 in timerSourcePrepareHelper (src=<optimized out>, timeout=0xb2a9f0bc) at kernel/qeventdispatcher_glib.cpp:136
#6  0x089b0ebd in timerSourcePrepare (source=0xb2102040, timeout=<optimized out>) at kernel/qeventdispatcher_glib.cpp:169
#7  0x019e6872 in g_main_context_prepare () from /lib/i386-linux-gnu/libglib-2.0.so.0
#8  0x019e6faf in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#9  0x019e7201 in g_main_context_iteration () from /lib/i386-linux-gnu/libglib-2.0.so.0
#10 0x089b18e7 in QEventDispatcherGlib::processEvents (this=0xb2100468, flags=...) at kernel/qeventdispatcher_glib.cpp:426
#11 0x0897d50d in QEventLoop::processEvents (this=0xb2a9f240, flags=...) at kernel/qeventloop.cpp:149
#12 0x0897d7a9 in QEventLoop::exec (this=0xb2a9f240, flags=...) at kernel/qeventloop.cpp:204
#13 0x0886694c in QThread::exec (this=0xa062c40) at thread/qthread.cpp:501
#14 0x0895ab5d in QInotifyFileSystemWatcherEngine::run (this=0xa062c40) at io/qfilesystemwatcher_inotify.cpp:248
#15 0x08869de0 in QThreadPrivate::start (arg=0xa062c40) at thread/qthread_unix.cpp:298
#16 0x00a51d4c in start_thread () from /lib/i386-linux-gnu/libpthread.so.0
#17 0x05263ace in clone () from /lib/i386-linux-gnu/libc.so.6

Thread 1 (Thread 0xb76e3980 (LWP 3542)):
[KCrash Handler]
#7  QModelIndex (other=..., this=0xbfad44b0) at ../../include/QtCore/../../src/corelib/kernel/qabstractitemmodel.h:65
#8  QSortFilterProxyModel::parent (this=0x9e2ff78, child=...) at itemviews/qsortfilterproxymodel.cpp:1659
#9  0x002df708 in parent (this=0xbfad4500) at /usr/include/qt4/QtCore/qabstractitemmodel.h:393
#10 KIdentityProxyModel::parent (this=0x9ed6000, child=...) at ../../kdeui/itemviews/kidentityproxymodel.cpp:358
#11 0x002df708 in parent (this=0xbfad4560) at /usr/include/qt4/QtCore/qabstractitemmodel.h:393
#12 KIdentityProxyModel::parent (this=0x9ed78d8, child=...) at ../../kdeui/itemviews/kidentityproxymodel.cpp:358
#13 0x08974c13 in parent (this=<optimized out>) at kernel/qabstractitemmodel.h:393
#14 QAbstractItemModelPrivate::rowsAboutToBeInserted (this=0x9ee7288, parent=..., first=0, last=0) at kernel/qabstractitemmodel.cpp:575
#15 0x08978234 in QAbstractItemModel::beginInsertRows (this=0x9ed78d8, parent=..., first=0, last=0) at kernel/qabstractitemmodel.cpp:2417
#16 0x002e08aa in KIdentityProxyModelPrivate::_k_sourceRowsAboutToBeInserted (this=0x9ed8120, parent=..., start=0, end=0) at ../../kdeui/itemviews/kidentityproxymodel.cpp:700
#17 0x089956b1 in QMetaObject::activate (sender=0x9ed6000, m=0x8adc2b8, local_signal_index=4, argv=0xbfad4750) at kernel/qobject.cpp:3547
#18 0x089e7395 in QAbstractItemModel::rowsAboutToBeInserted (this=0x9ed6000, _t1=..., _t2=0, _t3=0) at .moc/release-shared/moc_qabstractitemmodel.cpp:190
#19 0x0897821c in QAbstractItemModel::beginInsertRows (this=0x9ed6000, parent=..., first=0, last=0) at kernel/qabstractitemmodel.cpp:2416
#20 0x002e08aa in KIdentityProxyModelPrivate::_k_sourceRowsAboutToBeInserted (this=0x9ed7090, parent=..., start=0, end=0) at ../../kdeui/itemviews/kidentityproxymodel.cpp:700
#21 0x089956b1 in QMetaObject::activate (sender=0x9e2ff78, m=0x8adc2b8, local_signal_index=4, argv=0xbfad48c0) at kernel/qobject.cpp:3547
#22 0x089e7395 in QAbstractItemModel::rowsAboutToBeInserted (this=0x9e2ff78, _t1=..., _t2=0, _t3=0) at .moc/release-shared/moc_qabstractitemmodel.cpp:190
#23 0x0897821c in QAbstractItemModel::beginInsertRows (this=0x9e2ff78, parent=..., first=0, last=0) at kernel/qabstractitemmodel.cpp:2416
#24 0x01426217 in QSortFilterProxyModelPrivate::insert_source_items (this=0x9e899e8, source_to_proxy=..., proxy_to_source=..., source_items=..., source_parent=..., orient=Qt::Vertical, emit_signal=true) at itemviews/qsortfilterproxymodel.cpp:683
#25 0x0142a7ec in QSortFilterProxyModelPrivate::source_items_inserted (this=0x9e899e8, source_parent=..., start=0, end=0, orient=Qt::Vertical) at itemviews/qsortfilterproxymodel.cpp:806
#26 0x0142abc0 in QSortFilterProxyModelPrivate::_q_sourceRowsInserted (this=0x9e899e8, source_parent=..., start=0, end=0) at itemviews/qsortfilterproxymodel.cpp:1280
#27 0x089956b1 in QMetaObject::activate (sender=0x9dd4a08, m=0x8adc2b8, local_signal_index=5, argv=0xbfad4b40) at kernel/qobject.cpp:3547
#28 0x089e73f5 in QAbstractItemModel::rowsInserted (this=0x9dd4a08, _t1=..., _t2=0, _t3=0) at .moc/release-shared/moc_qabstractitemmodel.cpp:197
#29 0x089784ae in QAbstractItemModel::endInsertRows (this=0x9dd4a08) at kernel/qabstractitemmodel.cpp:2433
#30 0x026b09d0 in Akonadi::EntityTreeModelPrivate::insertCollection (this=0x9e87688, collection=..., parent=...) at ../../akonadi/entitytreemodel_p.cpp:713
#31 0x026b5d36 in Akonadi::EntityTreeModelPrivate::monitoredCollectionAdded (this=0x9e87688, collection=..., parent=...) at ../../akonadi/entitytreemodel_p.cpp:750
#32 0x026a4ae0 in qt_static_metacall (_a=0xbfad4d94, _id=19, _o=0x9dd4a08, _c=<optimized out>) at ./entitytreemodel.moc:138
#33 Akonadi::EntityTreeModel::qt_static_metacall (_o=0x9dd4a08, _c=QMetaObject::InvokeMetaMethod, _id=19, _a=0xbfad4d94) at ./entitytreemodel.moc:113
#34 0x089956b1 in QMetaObject::activate (sender=0x9e74068, m=0x28142f8, local_signal_index=6, argv=0xbfad4d94) at kernel/qobject.cpp:3547
#35 0x026f676d in Akonadi::Monitor::collectionAdded (this=0x9e74068, _t1=..., _t2=...) at ./monitor.moc:231
#36 0x026faf37 in Akonadi::MonitorPrivate::emitCollectionNotification (this=0x9e833e8, msg=..., col=..., par=..., dest=...) at ../../akonadi/monitor_p.cpp:600
#37 0x026fcd79 in Akonadi::MonitorPrivate::emitNotification (this=0x9e833e8, msg=...) at ../../akonadi/monitor_p.cpp:285
#38 0x0264bc39 in Akonadi::ChangeRecorderPrivate::emitNotification (this=0x9e833e8, msg=...) at ../../akonadi/changerecorder_p.h:60
#39 0x026fcf16 in Akonadi::MonitorPrivate::flushPipeline (this=0x9e833e8) at ../../akonadi/monitor_p.cpp:429
#40 0x026fcfb0 in Akonadi::MonitorPrivate::dataAvailable (this=0x9e833e8) at ../../akonadi/monitor_p.cpp:438
#41 0x026f6f33 in qt_static_metacall (_a=0xbfad5070, _id=23, _o=0x9e74068, _c=<optimized out>) at ./monitor.moc:137
#42 Akonadi::Monitor::qt_static_metacall (_o=0x9e74068, _c=QMetaObject::InvokeMetaMethod, _id=23, _a=0xbfad5070) at ./monitor.moc:108
#43 0x089956b1 in QMetaObject::activate (sender=0x9e9f670, m=0x2812e3c, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3547
#44 0x0269bd45 in Akonadi::EntityCacheBase::dataAvailable (this=0x9e9f670) at ./entitycache_p.moc:102
#45 0x026523ee in Akonadi::EntityCache<Akonadi::Collection, Akonadi::CollectionFetchJob, Akonadi::CollectionFetchScope>::processResult (this=0x9e9f670, job=0xa2139f8) at ../../akonadi/entitycache_p.h:192
#46 0x0269bd8e in qt_static_metacall (_a=0xbfad5218, _o=0x9e9f670, _c=<optimized out>, _id=<optimized out>) at ./entitycache_p.moc:54
#47 Akonadi::EntityCacheBase::qt_static_metacall (_o=0x9e9f670, _c=QMetaObject::InvokeMetaMethod, _id=1, _a=0xbfad5218) at ./entitycache_p.moc:47
#48 0x089956b1 in QMetaObject::activate (sender=0xa2139f8, m=0x9804ac, local_signal_index=3, argv=0xbfad5218) at kernel/qobject.cpp:3547
#49 0x007cb7b5 in KJob::result (this=0xa2139f8, _t1=0xa2139f8) at ./kjob.moc:208
#50 0x007cb808 in KJob::emitResult (this=0xa2139f8) at ../../kdecore/jobs/kjob.cpp:318
#51 0x026f272e in Akonadi::JobPrivate::delayedEmitResult (this=0xa691b88) at ../../akonadi/job.cpp:144
#52 0x08990c01 in QMetaCallEvent::placeMetaCall (this=0xa5a4aa0, object=0xa2139f8) at kernel/qobject.cpp:525
#53 0x08999c7b in QObject::event (this=0xa2139f8, e=0xa5a4aa0) at kernel/qobject.cpp:1195
#54 0x00ddfed4 in notify_helper (e=0xa5a4aa0, receiver=0xa2139f8, this=0x9aab328) at kernel/qapplication.cpp:4559
#55 QApplicationPrivate::notify_helper (this=0x9aab328, receiver=0xa2139f8, e=0xa5a4aa0) at kernel/qapplication.cpp:4531
#56 0x00de530d in QApplication::notify (this=0xa5a4aa0, receiver=0xa2139f8, e=0xa5a4aa0) at kernel/qapplication.cpp:4288
#57 0x0032b401 in KApplication::notify (this=0xbfad5a54, receiver=0xa2139f8, event=0xa5a4aa0) at ../../kdeui/kernel/kapplication.cpp:311
#58 0x0897e97e in QCoreApplication::notifyInternal (this=0xbfad5a54, receiver=0xa2139f8, event=0xa5a4aa0) at kernel/qcoreapplication.cpp:876
#59 0x08982ad8 in sendEvent (event=<optimized out>, receiver=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
#60 QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x9a80ab8) at kernel/qcoreapplication.cpp:1500
#61 0x08982e0c in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1393
#62 0x089b1494 in sendPostedEvents () at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:236
#63 postEventSourceDispatch (s=0x9aa9d00) at kernel/qeventdispatcher_glib.cpp:279
#64 0x019e6d86 in g_main_context_dispatch () from /lib/i386-linux-gnu/libglib-2.0.so.0
#65 0x019e7125 in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#66 0x019e7201 in g_main_context_iteration () from /lib/i386-linux-gnu/libglib-2.0.so.0
#67 0x089b1887 in QEventDispatcherGlib::processEvents (this=0x9a81800, flags=...) at kernel/qeventdispatcher_glib.cpp:424
#68 0x00e98aaa in QGuiEventDispatcherGlib::processEvents (this=0x9a81800, flags=...) at kernel/qguieventdispatcher_glib.cpp:204
#69 0x0897d50d in QEventLoop::processEvents (this=0xbfad59b4, flags=...) at kernel/qeventloop.cpp:149
#70 0x0897d7a9 in QEventLoop::exec (this=0xbfad59b4, flags=...) at kernel/qeventloop.cpp:204
#71 0x08982eba in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1148
#72 0x00ddda74 in QApplication::exec () at kernel/qapplication.cpp:3820
#73 0x0804ac91 in main (argc=42020648, argv=0x9e899e8) at ../../../kontact/src/main.cpp:218


Reproducible: Sometimes

Steps to Reproduce:
1. Create a 'inbox' (Posteingang) subdir
2. Move mail there and then to another folder
3. Move the folder one level up, to 'Local folders' (Lokale Ordner)
Actual Results:  
See report


Linux Mint 13 KDE
One POP3 in, One SMTP out (web.de)