mine did that too at first. but i worked the card several times in and out and it pops out reliably now. i thought to was stuck when it first happened but it has not done it since. both slots pop out the same now with any card i pop in. i like the way the card is retained even after it is ejected as there is no chance of it falling out without a positive action on my part to remove it.
I'm kind of new to this myself. Been a "Nikonian" only two days. Had my 7000 about 6 months now. In my limited experience, it seems to have a lot to do with the card that you use. Some cards seem to fit a little snugger than others, and slot 2 does seem to be a bit tighter than slot 1 for some reason.
my eyefi card and UPS-I cards seemed a tiny bit thicker then the other cards, i used a razor knife, and just scrapped a little bit, like sanded it with the razor, the pop in and out like a champ, UPS-I 45MB sandisk in no.1 slot for RAW, and the EYE-FI class 6 for uploading the JPG's