Zoomed text uses hinting from unzoomed text and looks ugly

Using the 'fontanatomy' application (see http://labs.trolltech.com/blogs/2008/08/28/font-anatomy/) you can zoom in on some text as drawn by QTextLayout by using the zoom option on QPainter.

When I expect is that a font is rendered based on the new pixel size.
What I get instead is something that appears to have the font hinting applied at the original pixel size and then scaled up.

Easiest way to show this is to take an Arial of 6pt with the text 'ma' and zoom it to a larger pixel size (but less than 64). The 'a' and the 'm' look quite distorted.

Downstream report (with screenshots) http://bugs.kde.org/186513