On Mac OS X (10.7.5), when popping a QFileDialog::getSaveFileName AND specifying a folder, then the application will crash on close event. If no folder is specified (NULL), then the application exit normally on close event.
This happen everytime, wether you choose to "Save" or "Cancel" the dialog, as soon as the application close event happen.

Apple crash report:

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libobjc.A.dylib 0x00007fff938b838d objc_msgSend_vtable14 + 13
1 com.apple.AppKit 0x00007fff8a91ef52 -[NSImage _deallocAuxiliaryStorage] + 58
2 com.apple.AppKit 0x00007fff8a91ed6a -[NSImage dealloc] + 166
3 libobjc.A.dylib 0x00007fff938bc03c (anonymous namespace)::AutoreleasePoolPage::pop(void*) + 434
4 com.apple.CoreFoundation 0x00007fff9146f915 _CFAutoreleasePoolPop + 37
5 com.apple.Foundation 0x00007fff8fb0b4f9 -[NSAutoreleasePool release] + 154
6 libqcocoa.dylib 0x000000010530cb69 QCocoaWindow::~QCocoaWindow() + 233
7 libqcocoa.dylib 0x000000010530ca4f QCocoaWindow::~QCocoaWindow() + 15
8 QtGui 0x000000010156c050 QWindow::destroy() + 256
9 QtWidgets 0x0000000101b602c2 QWidgetPrivate::deleteTLSysExtra() + 50
10 QtWidgets 0x0000000101b60138 QWidget::destroy(bool, bool) + 888
11 QtWidgets 0x0000000101b37ab3 QWidget::~QWidget() + 1443
12 QtWidgets 0x0000000101cd3f9b QDialog::~QDialog() + 43
13 SpectraLayers 0x000000010003fbb9 MainWindow::ShowStartDialog() + 41
14 SpectraLayers 0x0000000100075621 LayersGui::Close() + 1841
15 SpectraLayers 0x000000010003ebb2 MainWindow::closeEvent(QCloseEvent*) + 34