sd card and cover cache

i started using a brand new sd card with pdf books... i know the kobo is supposed to generate and store covers in a cache on the sd cards but this doesn't happen and every time i turn on the kobo it generates them slowly

in addition, on boot, the homepage is blank and i have to click the home button to see the last books

something buggy?!? ... kobo touch, firmware 2.5.2... thanks