Aperture misbehaves: images that can't be moved between projects

I have a  set of images in Aperture that cannot be moved between projects. If I try to move them they are copied.

I’ve repaired permissions and done the standard database repair to no effect.

I’ve inspected the images in the Finder by exploring the Package contents and searching on the Aperture provided file names — they appear unremarkable. 

I’m afraid something in my Aperture database is broken, but I’m reluctant to do a full database restoration. I don’t know how much data will be lost. 

I fear multiple backups and a full database rebuild are in my future…

Update 

I researched this a bit, glad that a few old Aperture sites are still around. Two useful references:

• Get help with Aperture 3 - Apple Support: Apple’s cumulative troubleshooting document
• How do I repair or rebuild my Aperture library or permissions? | PhotosApps.Expert

I think I’ll try importing into a new project. I have a 500 GB Library on a 1TB SSD, but I can start the import into a peripheral drive tonight.

Remember when database/file system corruption was a solved problem?