Star ratings in camera sometimes don't import into Lightroom

Hi,

As part of my workflow, I often rate images in-camera using the "Rate" button on the 5D3.
Usually these ratings are imported into Lightroom. Sometimes they're not.

I have a hunch that it has something to do with the card I'm using to playback images. I'm saving raws to the SD card and jpeg backups to the CF card*, and playing back (and rating) the raws on the SD card. Sometimes I take out the SD card just to see what's on the CF card before I format it - maybe that reverts the "playback" card to the CF instead of the SD, and screws up the ratings at the same time?

I can't quite put my finger on the problem.

Any thoughts?
Thanks,
Nathan

* because I have a bunch of large SD cards but only a couple of small CF cards.