1.5.7 locked into low res on mac osx mavericks

Hi,

just installed 1.5.7 on mavericks. It shows in low res so the font is all pixelated which isn't nice for programming. When I try to change the properies I find that low res is ticked but disabled (greyed out) so I can't change it. Even when I unpadlock the app.

anyone else got this or an idea how to solve it