The D7000 decides what goes where and on what card. It anticipates what is coming and where its going to put it. Your RAW files in "slot 1" is only a preference. If the camera thinks its going to need more room and your card in SLOT 1 is not big enought it will put it in slot 2. I found 2 things. 1. stop using 2 different size cards and or 2. buy bigger cards. I NEVER have this problem because I do not leave my photos on my cards and I re-format everytime I unload them. Also just because it worked for you one time it shouldn't be such a shock if it doesnt work again. RAW files are never the same size from one photo shoot to the next.