Confirming this problem on Ubuntu 14.04 with Clementine 1.2.3~trusty from PPA.

Here comes backtrace from gdb with core dumped:

#0  0x00002b80089f8e29 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#1  0x00002b80089ff4a0 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#2  0x00002b8005c8e4dd in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3  0x00002b8008a42a11 in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#4  0x00002b8008a43440 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#5  0x00002b8008a425cc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#6  0x00002b8008a43440 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#7  0x00002b8008a425cc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#8  0x00002b8008a43440 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#9  0x00002b8008a425cc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#10 0x00002b8008a43440 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#11 0x00002b8008a425cc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#12 0x00002b8008a43440 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#13 0x00002b8008a425cc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#14 0x00002b8008a43440 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevice*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#15 0x00002b8008a425cc in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#16 0x00002b8008c058ae in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#17 0x00002b8008a37ea0 in QWidgetPrivate::syncBackingStore() () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#18 0x00002b8008a47e6a in QWidget::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#19 0x00002b8008e029b3 in QMainWindow::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#20 0x00002b80089f8e2c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#21 0x00002b80089ff4a0 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#22 0x00002b8005c8e4dd in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#23 0x00002b8005c91b3d in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#24 0x00002b8005cbbf83 in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#25 0x00002b8007634e04 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#26 0x00002b8007635048 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#27 0x00002b80076350ec in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#28 0x00002b8005cbb7a1 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#29 0x00002b8008a9abb6 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#30 0x00002b8005c8d0af in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#31 0x00002b8005c8d3a5 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#32 0x00002b8005c92b79 in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#33 0x000000000094ed25 in main ()

Using libqtgui4 4:4.8.5+git192-g085f851+dfsg-2ubuntu4.

However, the same operation works fine with Clementine 1.2.0+dfsg-2build1 (libqtgui4 is the same).