Comment 2 for bug 735746

The issue is the icon /usr/share/icons/hicolor/48x48/apps/gbrainy.png is actually a 32x32 icon.

The bug appears to be in data/Makefile.am as it installs data/app-graphics/gbrainy.png into the 48x48 dir. Guessing you need to make gbrainy32.png and gbrainy48.png.