Motion 5 Graphic won't key in FCP 7

I'm using Motion 5 to create some title graphics, then importing to FCP7. However, they won't key. I've tried ProRes 422 HQ, and uncompressed 8 bit 422, but FCP 7 doesn't recognize the alpha channel. What am I doing wrong? When I use Motion 4, it's automatic. Motion 5 has cooler fx, so I'm trying to get more familiar with it.