Qt crash when showing a tooltip

My Qt application keeps on crashing when the tooltip in the attached file is shown.

To reproduce the problem just set a widget tooltip in the following way:

QFile file("tooltip.txt");
file.open(QIODevice::ReadOnly);
QTextStream stream(&file);
QString tooltipText = stream.readAll();
file.close();
myWidget->setToolTip(tooltipText);

I'm using the latest version of Qt (4.6.3) on Windows

This is part of the Call Stack when the crash happens:

QtGuid4.dll!`anonymous namespace'::LineBreakHelper::currentGlyph() Line 1683 + 0x1a bytes C++
QtGuid4.dll!`anonymous namespace'::LineBreakHelper::adjustRightBearing() Line 1692 + 0xe bytes C++
QtGuid4.dll!QTextLine::layout_helper(int maxGlyphs=2147483647) Line 1931 C++
QtGuid4.dll!QTextLine::setLineWidth(double width=8388607.0000000000) Line 1602 C++
QtGuid4.dll!qt_format_text(const QFont & fnt=

{...}, const QRectF & _r={...}

, int tf=134218769, const QTextOption * option=0x00000000, const QString & str=

{...}, QRectF * brect=0x00000000, int tabstops=48, int * __formal=0x00000000, int tabarraylen=0, QPainter * painter=0x0012cb54) Line 7747 C++
QtGuid4.dll!QPainter::drawText(const QRect & r={...}

, int flags=1041, const QString & str=

{...}, QRect * br=0x00000000) Line 5807 + 0x41 bytes C++
QtGuid4.dll!QStyle::drawItemText(QPainter * painter=0x0012cb54, const QRect & rect={...}

, int alignment=1041, const QPalette & pal=

{...}, bool enabled=true, const QString & text={...}

, QPalette::ColorRole textRole=ToolTipText) Line 541 C++
QtGuid4.dll!QLabel::paintEvent(QPaintEvent * __formal=0x0012d3f0) Line 1038 C++
QtGuid4.dll!QTipLabel::paintEvent(QPaintEvent * ev=0x0012d3f0) Line 230 C++
QtGuid4.dll!QWidget::event(QEvent * event=0x0012d3f0) Line 8191 C++
.....