This has nothing to do with Grub. All grub does is pass control to the windows boot loader. But Windows Vista screwing around with the USB filesyetm, is a Vista issue (maybe you have Vista's ReadBoost on) .
This has nothing to do with Grub. All grub does is pass control to the windows boot loader. But Windows Vista screwing around with the USB filesyetm, is a Vista issue (maybe you have Vista's ReadBoost on) .