Mountain Lion on MBP Retina keeps using low res icons

Hi,

I have a MacBook Pro Retina and until today all was fine. I added an icon to a pen drive and it showed cristal clear at 36x36 setting.

Now I initialised that same pen drive and readded the very same icon, but now I don't get a crystal clear one. Instead it is very blurry. I tried other icons and devices, too (ext hd, normal folder, etc) but the result is the same. I keep getting blurred icons and what is worse is that

Anyone can help me?