CLONE -drawPoint: point is only occasionally painted if set to Qt::SquareCap

This issue seems to be strongly related to QTBUG-6721.

I'm running Qt 4.6.3 on Windows (vs2005). My application draws points using

QPainter *p = ...;
pen.setWidth(250);
pen.setColor(Qt::red);
pen.setCapStyle(Qt::SquareCap);
p->setPen(pen);
for (pt in points)

When using Qt::SquareCap, points are only actually drawn at random. Very few points are occasionally visible, most of them aren't, but it's not deterministic.
When changing to Qt::RoundCap, all points show up just fine.
I did not have this problem in Qt 4.5.
Hopefully I'll find the time to build a small testcase this weekend.

Best regards,
Jan