QSortFilterProxyModel crashed at mapToSource function in Qt 4.8.4

I use QFileSystemModel to show the directory and files. Also own class FileListModel inherits QSortFilterProxyModel. I want to only show the "html" files in my QTreeView.

I added a SLOT to connect with doubleClicked(QModelIndex) signal. In the slot:

Code:

QModel index = proxyModel->mapToSource(currentIndex);
if(!index.isValid())
{
    return;
}

But if I click the QTreeView items quickly, it maybe crash at

Code:

proxyModel->mapToSource(currentIndex);

I don't know why.

And here is the call stack and screenshots:
Attachment 9294 Attachment 9295

Code:

>	QtGuid4.dll!QSortFilterProxyModelPrivate::index_to_iterator(const QModelIndex & proxy_index)  Line 193 + 0x8 bytes	C++
 	QtGuid4.dll!QSortFilterProxyModelPrivate::proxy_to_source(const QModelIndex & proxy_index)  Line 369	C++
 	QtGuid4.dll!QSortFilterProxyModel::mapToSource(const QModelIndex & proxyIndex)  Line 2519 + 0x10 bytes	C++
 	TBXXA.exe!MainWindow::onSaveBtnClicked()  Line 341 + 0x2a bytes	C++
 	TBXXA.exe!MainWindow::onTreeViewDoubleClicked(const QModelIndex & index)  Line 452	C++
 	TBXXA.exe!MainWindow::qt_static_metacall(QObject * _o, QMetaObject::Call _c, int _id, void * * _a)  Line 84	C++
 	QtCored4.dll!QMetaObject::activate(QObject * sender, const QMetaObject * m, int local_signal_index, void * * argv)  Line 3539 + 0x2e bytes	C++
 	QtGuid4.dll!QAbstractItemView::doubleClicked(const QModelIndex & _t1)  Line 355 + 0x15 bytes	C++
 	QtGuid4.dll!QTreeView::mouseDoubleClickEvent(QMouseEvent * event)  Line 1878	C++
 	QtGuid4.dll!QWidget::event(QEvent * event)  Line 8380	C++
 	QtGuid4.dll!QFrame::event(QEvent * e)  Line 557 + 0xc bytes	C++
 	QtGuid4.dll!QAbstractScrollArea::viewportEvent(QEvent * e)  Line 1043 + 0xc bytes	C++
 	QtGuid4.dll!QAbstractItemView::viewportEvent(QEvent * event)  Line 1645	C++
 	QtGuid4.dll!QTreeView::viewportEvent(QEvent * event)  Line 1258	C++
 	QtGuid4.dll!QAbstractScrollAreaPrivate::viewportEvent(QEvent * event)  Line 100 + 0x28 bytes	C++
 	QtGuid4.dll!QAbstractScrollAreaFilter::eventFilter(QObject * o, QEvent * e)  Line 116 + 0x29 bytes	C++
 	QtCored4.dll!QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject * receiver, QEvent * event)  Line 1056 + 0x15 bytes	C++
 	QtGuid4.dll!QApplicationPrivate::notify_helper(QObject * receiver, QEvent * e)  Line 4558 + 0x11 bytes	C++
 	QtGuid4.dll!QApplication::notify(QObject * receiver, QEvent * e)  Line 4105 + 0x2f bytes	C++
 	QtCored4.dll!QCoreApplication::notifyInternal(QObject * receiver, QEvent * event)  Line 946 + 0x15 bytes	C++
 	QtCored4.dll!QCoreApplication::sendSpontaneousEvent(QObject * receiver, QEvent * event)  Line 234 + 0x38 bytes	C++
 	QtGuid4.dll!QApplicationPrivate::sendMouseEvent(QWidget * receiver, QMouseEvent * event, QWidget * alienWidget, QWidget * nativeWidget, QWidget * * buttonDown, QPointer<QWidget> & lastMouseReceiver, bool spontaneous)  Line 3171 + 0xe bytes	C++
 	QtGuid4.dll!QETWidget::translateMouseEvent(const tagMSG & msg)  Line 3365 + 0x2a bytes	C++
 	QtGuid4.dll!QtWndProc(HWND__ * hwnd, unsigned int message, unsigned int wParam, long lParam)  Line 1698 + 0xc bytes	C++
 	user32.dll!7689c4e7() 	
 	[Frames below may be incorrect and/or missing, no symbols loaded for user32.dll]	
 	user32.dll!7689c5e7() 	
 	user32.dll!7689c590() 	
 	user32.dll!7689cc19() 	
 	user32.dll!7689cc70() 	
 	QtCored4.dll!QEventDispatcherWin32::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags)  Line 810	C++
 	QtGuid4.dll!QGuiEventDispatcherWin32::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags)  Line 1204 + 0x15 bytes	C++
 	QtCored4.dll!QEventLoop::processEvents(QFlags<enum QEventLoop::ProcessEventsFlag> flags)  Line 150	C++
 	QtCored4.dll!QEventLoop::exec(QFlags<enum QEventLoop::ProcessEventsFlag> flags)  Line 204 + 0x2d bytes	C++
 	QtCored4.dll!QCoreApplication::exec()  Line 1218 + 0x15 bytes	C++
 	QtGuid4.dll!QApplication::exec()  Line 3824	C++
 	TBXXA.exe!main(int argc, char * * argv)  Line 32 + 0x6 bytes	C++
 	TBXXA.exe!WinMain(HINSTANCE__ * instance, HINSTANCE__ * prevInstance, char * __formal, int cmdShow)  Line 131 + 0x12 bytes	C++
 	TBXXA.exe!__tmainCRTStartup()  Line 547 + 0x2c bytes	C
 	TBXXA.exe!WinMainCRTStartup()  Line 371	C
 	kernel32.dll!75fbed6c() 	
 	ntdll.dll!76e6377b() 	
 	ntdll.dll!76e6374e()