whs

Well, it is designed like that on purpose. The basic idea is that the Vista media system will not import pictures from a card twice. E.g. you import the first pictures that you took on Monday and then you take some more pictures during the week and stick the card again in on Sturday. At that point you do not want the Monday pictures imported again - just the new ones.
However, if you handle the card like a folder and transfer the Saturday pictures manually, the Monday pictures should not be referred to.