crash in designer on Mac OS X / Cocoa

Here is the backtrace:

0 libobjc.A.dylib 0x00007fff800191ac objc_msgSend_vtable4 + 12
1 com.apple.AppKit 0x00007fff844457a3 -[NSView _endEditingIfFirstResponderIsASubview] + 96
2 com.apple.AppKit 0x00007fff8444547f -[NSView removeFromSuperview] + 61
3 QtGui 0x0000000100027e15 qt_mac_destructView(NSView*) + 373
4 QtGui 0x0000000100028cd6 QWidget::destroy(bool, bool) + 2006
5 QtGui 0x00000001000e72ec QWidget::~QWidget() + 876
6 QtGui 0x00000001004af34c QToolBar::~QToolBar() + 108
7 QtCore 0x0000000100c83f7f QObjectPrivate::deleteChildren() + 95
8 QtGui 0x00000001000e72d2 QWidget::~QWidget() + 850
9 com.yourcompany.dlg 0x00000001000023fe Dialog::~Dialog() + 50 (main.cpp:19)
10 com.yourcompany.dlg 0x0000000100002b9b W::fla() + 57 (main.cpp:65)
11 com.yourcompany.dlg 0x0000000100002070 W::qt_metacall(QMetaObject::Call, int, void**) + 82 (main.moc:133)
12 QtCore 0x0000000100c851d6 QMetaObject::activate(QObject*, QMetaObject const*, int, void**) + 630
13 QtGui 0x00000001006adc11 QAbstractButton::clicked(bool) + 49
14 QtGui 0x00000001003ed880 QAbstractButtonPrivate::emitClicked() + 64
15 QtGui 0x00000001003eea2a QAbstractButtonPrivate::click() + 154
16 QtGui 0x00000001003eec7f QAbstractButton::mouseReleaseEvent(QMouseEvent*) + 111
17 QtGui 0x00000001000e6220 QWidget::event(QEvent*) + 2016
18 QtGui 0x00000001003edac8 QAbstractButton::event(QEvent*) + 40
19 QtGui 0x0000000100484625 QPushButton::event(QEvent*) + 69
20 QtGui 0x000000010008c77d QApplicationPrivate::notify_helper(QObject*, QEvent*) + 189
21 QtGui 0x0000000100092ea0 QApplication::notify(QObject*, QEvent*) + 7392
22 QtCore 0x0000000100c7f37c QCoreApplication::notifyInternal(QObject*, QEvent*) + 124
23 QtGui 0x000000010008c8fc qt_sendSpontaneousEvent(QObject*, QEvent*) + 44
24 QtGui 0x0000000100044ed6 qt_mac_handleMouseEvent(void*, void*, QEvent::Type, Qt::MouseButton) + 1478
25 QtGui 0x00000001000335a8 -[QCocoaView mouseUp:] + 40
26 com.apple.AppKit 0x00007fff8451c719 -[NSWindow sendEvent:] + 5547
27 QtGui 0x000000010003ce5c -[QCocoaWindow sendEvent:] + 940
28 com.apple.AppKit 0x00007fff84451e22 -[NSApplication sendEvent:] + 4719
29 com.apple.AppKit 0x00007fff843e8796 -[NSApplication run] + 474
30 QtGui 0x000000010004a102 QEventDispatcherMac::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 2050
31 QtCore 0x0000000100d56ee4 QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 68
32 QtCore 0x0000000100d571f4 QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 180
33 QtCore 0x0000000100d5881c QCoreApplication::exec() + 188
34 com.yourcompany.dlg 0x000000010000225b main + 61 (main.cpp:75)
35 com.yourcompany.dlg 0x0000000100001ee4 start + 52