Comment 3 for bug 376657

The icons contain multiple layers, 16x16, 32x32 and 48x48. It looks like vista is taking the small format and extrapolating that as opposed to start form a 32x32 or 48x48 layer which would scale up better.

See for instance http://bazaar.launchpad.net/%7Eubuntu-installer/wubi/trunk/annotate/head%3A/data/images/Wubi.ico