Same issue here.
I discovered that if you close iPhoto and delete the com.apple.iPhoto.plist in your library file then restart iPhoto, & while in your unnamed faces album go to the top menu bar:- /photos/detect missing faces then
the photo will disappear (presumably because it has no missing faces)
an unnamed square will pop up, which can be deleted and then the photo disappears (because it now has no missing faces).
So this seems to be a problem of corrupt indexing somehow?
While this works it is a bit cumbersome on large Libraries. I wish there was a batch method of doing this.
I've been having the same problem of photos being in an Unnamed Smart Album despite there being no box/face to name in the photo itself. This is using iPhoto 9.6, OS X 10.10.1 on an iMac. I've found 2 things that will remove the unnamed face, but keeps Keywords and named faces in place. Unfortunately the photos have to be done one by one:
1. Click on "Reprocess Raw" in the Edit window. I'm assuming this one will only work if the original photo is RAW. Suspect you would also lose any other edits you have made to the photo, but it does keep keywords and named faces.
2. Duplicate the photo (e.g. Command+D). The duplicated photo retains keywords, named faces (and i'm assuming other edits) but it doesn't have the mystery unnamed face. You can then delete the first copy and rename the second copy (i.e. delete the "Version 2" in the file name)