Applicatio crash when draw text

My application crash when use drawtext (under mac osx lion with qt-4.8.0 release)
It crash when call
painter->drawText(m_rect, Qt::TextWordWrap | Qt::AlignTop | Qt::AlignHCenter, m_strContent);

/*************** my code ******************/
void Comment::Draw(QPainter* painter, const QRectF& clip)
{
painter->save();
painter->setClipRect(clip);
painter->setPen(QColor(0,0,0,50));

//Draw text
painter->setFont(m_font);
painter->drawText(m_rect, Qt::TextWordWrap | Qt::AlignTop | Qt::AlignHCenter, m_strContent);
painter->restore();
}

/*************** the crash report ******************/

Code Type: X86-64 (Native)
Parent Process: launchd [152]

Date/Time: 2011-12-17 14:37:40.914 +0800
OS Version: Mac OS X 10.7.2 (11C74)
Report Version: 9

Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x00007fff5fc00000

VM Regions Near 0x7fff5fc00000:
Stack 00007fff5f400000-00007fff5fc00000 [ 8192K] rw-/rwx SM=COW thread 0
-->
__TEXT 00007fff6015a000-00007fff6018f000 [ 212K] r-x/rwx SM=COW /usr/lib/dyld

Application Specific Information:
objc[282]: garbage collection is OFF

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 QtGui 0x00000001005b75e8 QTextEngine::shape(int) const + 1160
1 QtGui 0x00000001005c3f8f QTextLine::draw(QPainter*, QPointF const&, QTextLayout::FormatRange const*) const + 1087
2 QtGui 0x00000001004b944c QPainter::setClipRect(QRectF const&, Qt::ClipOperation) + 5500
3 QtGui 0x00000001004b9a74 QPainter::drawText(QRectF const&, int, QString const&, QRectF*) + 180
4 tw.idv.swordsoft.Layout 0x0000000100097d55 SwordSoft::Comment::Draw(QPainter*, QRectF const&) + 1221
5 tw.idv.swordsoft.Layout 0x000000010002a996 MainDoc::Draw(QPainter*, QRectF const&) + 1510
6 tw.idv.swordsoft.Layout 0x0000000100025f57 MainView::paintEvent(QPaintEvent*