okay i know this gunna be werid but this does happen..
if theres money on ur cc and not on paypal it takes from card, if theres money from paypal it takes from tht, if theres money in both, say 12 in paypal and 3 in credit card it takes from paypal, if u wanna buy something tht is 15 and only have 12 in paypal u cant buy even though u have 3 in card, i duno why it just works like tht, i only know this cause i asked paypal when i called =]
yw