Why has Empty iPhoto Trash stopped working reliably?

There have been several instances in the last couple of months when I have selected Empty iPhoto Trash and the photos in iPhoto's Trash disappeared (as expected), but the underlying files were not moved to the Finder Trash. The first few of times this happened, I thought I might have just gone crazy, perhaps having emptied the iPhoto trash immediately, subsequently, and unconsciously, especially because on other occasions, the deleted iPhoto files correctly were/are moved to the Finder Trash. It's sneakily tricky to verify, becuase once you have emptied the trash, you've lost the record of the filenames of the should-have-been-deleted files, which makes it difficult to go back and check if those files still exist on your disk (by searching for filename within the iPhoto Library package).

But I have now verified on several follow-up instances that this does happen (Empty iPhoto Trash appears to work, iPhoto Trash is visibly cleared, nothing is moved to Finder Trash) and that the files are remaining in the iPhoto Library package (forever taking up disk space) but not actually viewable in iPhoto.

Has this occured to anyone else? It seems that it's only been happening to me in the recent month or two, and I don't believe it's been occuring all the way back to the mid-December 2013 release date of the latest update (9.5.1) to iPhoto, but I'm not exactly sure when this issue started for me.

I have both Repaired and Rebuilt my iPhoto Library, the second time going through this process to see if I could at least find these zombie (undeleted) files and re-delete them:

http://arstechnica.com/apple/2013/08/deleting-zombie-photos-from-iphoto/

I found nothing, no files/pictures were apparently recovered, but since at the time (unlike now) I did not have any specific filenames to check if they were missed by the Repair/Rebuild processes, I'll give it a try again.

I'll submit this as a bug report too, but wanted to post it here in case others 1) might be having the same problem, too, 2) can shed light on what might be happening here and how to fix it.