Touch offset on QNX since 5.3.1

This may be a query rather than a bug report!
Since using Qt5.3.1 (and later) we have experienced an offset on the touchscreen. The size of the offset seems to be a quarter-width and quarter-height of the screen. The point activated in Qt is above and to the left of the point touched. The arrival of the problem seems to be related to commit 0x592d79fc which added an offset and a size into a call to QRectF:

m_touchPoints[touchId].area = QRectF(w->geometry().left() + windowPos[0] - (touchArea[0]>>1), w->geometry().top()  + windowPos[1] - (touchArea[1]>>1), (touchArea[0]>>1), (touchArea[1]>>1));

If we remove the "touchArea" parts of the first and second arguments, and set the third and fourth arguments to zero, we get a correctly calibrated touchscreen.
We would happily accept that this change was correct if we could be guided to some setting we need to change within Qt or Screen that corrects for it.