Photos replaced with blanks & phantom photo?

I am operating IPhoto 9.2.1 with Mac 10.7.3. We have a number of eventswith over 12,000 photos and in the problem event I have about 100 photos. We imported six photos from our camera today and merged them into that event. Now, about 12-15 other photos (NOT the ones we imported) in that event show a blank box. However, when the cursor is moved over them they briefly show a photo from an entirely different event that was created over 6 months ago.

We removed the photo showing as the phantom into trash and emptied the trash, rebooted and yet this still happens. When I open a photo in that event and see the thumbnails along the bottom, the phantom photo appears over the 12-15 affected photos. But when I click on the thumbnail, the correct photo opens.

I have tried repairing the library but nothing changes.