Null pointer dereferene in QGLContextPrivate::contextGroup()

Sometimes Qt will crash at QGLContextPrivate::contextGroup() due to NULL pointer dereference (ctx->d_ptr) when I call QPainter::drawText() to render text under GL2 painter engine in Qt-4.8.0, Qt-4.7.x is not affected by this problem. Below is the call stack at the time the crash occur:

QtCored4.dll!qt_message_output(QtMsgType msgType, const char * buf) Line 2243 C++
QtCored4.dll!qt_message(QtMsgType msgType, const char * msg, char * ap) Line 2301 + 0x19 bytes C++
QtCored4.dll!qFatal(const char * msg, ...) Line 2485 C++
QtCored4.dll!qt_assert(const char * assertion, const char * file, int line) Line 2000 C++
QtOpenGLd4.dll!QScopedPointer<QGLContextPrivate,QScopedPointerDeleter<QGLContextPrivate> >::operator->() Line 112 + 0x25 bytes C++
> QtOpenGLd4.dll!QGLContextPrivate::contextGroup(const QGLContext * ctx) Line 453 + 0x1a bytes C++
QtOpenGLd4.dll!QGLContextGroupResourceBase::value(const QGLContext * context) Line 5688 + 0xa bytes C++
QtOpenGLd4.dll!QGLContextGroupResource<QGLGlyphTexture>::value(const QGLContext * context) Line 763 + 0xf bytes C++
QtOpenGLd4.dll!QGLTextureGlyphCache::width() Line 122 + 0x1f bytes C++
QtOpenGLd4.dll!QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyphType, QStaticTextItem * staticTextItem) Line 1639 + 0xd bytes C++
QtOpenGLd4.dll!QGL2PaintEngineEx::drawTextItem(const QPointF & p, const QTextItem & textItem) Line 1544 + 0x16 bytes C++
QtGuid4.dll!QPainter::drawTextItem(const QPointF & p, const QTextItem & _ti) Line 6683 C++
QtGuid4.dll!drawMenuText(QPainter * p, QFixed x, QFixed y, const QScriptItem & si, QTextItemInt & gf, QTextEngine * eng, int start, int glyph_start) Line 2042 C++
QtGuid4.dll!QTextLine::draw(QPainter * p, const QPointF & pos, const QTextLayout::FormatRange * selection) Line 2417 C++
QtGuid4.dll!qt_format_text(const QFont & fnt, const QRectF & _r, int tf, const QTextOption * option, const QString & str, QRectF * brect, int tabstops, int * ta, int tabarraylen, QPainter * painter) Line 8284 C++
QtGuid4.dll!QPainter::drawText(const QRect & r, int flags, const QString & str, QRect * br) Line 6200 C++

Unfortunately, I haven't found a way to write a simple program to reproduce this problem.