Trying to subtract one part from another

I'm trying to subtract one part from another to make a 3D printed holder for that part. I made filled surfaces for all the "holes" I could find to try and make the part solid for a combine/subtract feature. When I bring that part into the holder part, the part seems to have lost all the surface fills. What's going on here?

ORIGINAL PART

PART GETTING READY FOR THE COMBINE

SolidworksParts And Features