QPainter::drawPixmap : Grid is out of phase when zooming

Draw a Pixmap using drawPixmap.
Then Draw a grid for each pixel when you zoom into the image.
When you zoom in the image the grid gets out of phase.

Attached is an example application that shows this issue.

For zooming press CTRL and mouse wheel event.
Zoom the image to 18x then scroll to the right and you will see that the grid no longer match the pixels.