I have a KeyLab 25 and it works just fine in FL (save for the transports. Haven't figured those out yet!). I also tried a KeyLab 49 in the store, and it worked just fine.
If you haven't already, check the FL Midi settings. There may be something in there. I wouldn't get your money back yet, as the KeyLab is amazing. And if you've got a 49, that's even better than mine! I would have done a 49, but it didn't fit on my desk.
Best of luck to you!