Test spotlight importer reports wrong architecture

I am trying to test my spotlight importer for a custom file type. I am using mdimport with the -d option of a file. It does find a correct version of the importer (actually in a Debug build of my app bundle in the build location). However, it says it fails because it "does not match current 64 bit architecture". I do however have an Intel machine, calling it from Terminal.app running in 64 bit mode, and the importer plugin is build for the standard archs (64 bit universal and ppc). I have double checked that the x86_64 bit arch is actually included in the binary, and of course it is. Also, running mdls on the file returns nothing. However Spotlight is able to find the particular file. So what is going on? Are mdimport and mdls broken? How can I test the tests?

thanks,
Christiaan