Version is 15.04.3.

When editing video, often moving the playhead on the timeline causes whole X or KDE to close or crash. It's hard to tell whether it's the problem with KDEnlive itself or something wrong with the drivers, but at the time of crash I see the following line added in kernel log:

[ 2277.554290] kactivitymanage[3726]: segfault at 7f3209f4bd10 ip 00007f320b3a2881 sp 00007ffc25033af8 error 4 in libQt5Sql.so.5.5.0[7f320b38c000+41000]

When attached GDB to kactivitymanagerd, I got this stacktrace when everything collapses:
#0  0x00007f95db2a9881 in QSqlDatabase::close() () from /usr/lib/libQt5Sql.so.5
#1  0x00007f95db2aade9 in QSqlDatabase::~QSqlDatabase() () from /usr/lib/libQt5Sql.so.5
#2  0x00007f95db2ace1d in ?? () from /usr/lib/libQt5Sql.so.5
#3  0x00007f95f7726289 in QHashData::free_helper(void (*)(QHashData::Node*)) () from /usr/lib/libQt5Core.so.5
#4  0x00007f95db2a9553 in ?? () from /usr/lib/libQt5Sql.so.5
#5  0x00007f95f6f17f88 in __run_exit_handlers () from /usr/lib/libc.so.6
#6  0x00007f95f6f17fd5 in exit () from /usr/lib/libc.so.6
#7  0x00007f95ecf4834e in QXcbConnection::processXcbEvents() () from /usr/lib/libQt5XcbQpa.so.5
#8  0x00007f95f78d2eb1 in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#9  0x00007f95f78a3769 in QCoreApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#10 0x00007f95f78a389b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#11 0x00007f95f78a5c96 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#12 0x00007f95f78f9e33 in ?? () from /usr/lib/libQt5Core.so.5
#13 0x00007f95f36d39fd in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#14 0x00007f95f36d3ce0 in ?? () from /usr/lib/libglib-2.0.so.0
#15 0x00007f95f36d3d8c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#16 0x00007f95f78fa23f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#17 0x00007f95f78a126a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#18 0x00007f95f78a920c in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#19 0x0000000000412574 in main ()

lspci|grep -i vga
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09)

I tried attaching with GDB to kdenlive itself, but at the time of crash GDB only said that the process is no longer available.

Reproducible: Sometimes

Steps to Reproduce:
1. Create a project, add clips, move playhead.
2. Wait for it… wait for it… ;-)

I could reproduce the crash once by setting all thumbnails off and then setting audio thumbnails on and clicking "Ok" in the dialog.