Right ALT key not recognized

I have the following keypress event routine (Qt 4.7):

Code:

---

void GLTerrain::keyPressEvent(QKeyEvent *event)
{
switch (event->key()) {
		case Qt::Key_Shift:
			bShift=true;
			break;
		case Qt::Key_Alt:
			bAlt=true;
			if (bEnableAllBoundingBoxFeature==true)	bAllBoundingBox=true;
			break;
}

---

On OSX everything works fine, on Windows (VC++ 2008, 64bit), the right ALT key event is not triggered (only the left ALT is).
Any idea? Thanks

I forgot to tell that I checked the values returned by event->key(): the first time I press tha RIGHT ALT key, it returns the correct value (.....251); if I press it again, it returns ......249 (the CTRL key). How odd... and it's happening in Windows, OSX works just fine.