Faces thumbnails missing after recovery from time machine

Question

I got a new harddisk in my iMac via Apple's harddisk replacement program. I recovered all my data via a Time Machine backup (from a Time Capsule). All seemed fine after recovery of backup. When firing up iPhoto after the recovery iPhoto asks for updating all the thumbnails (don't know why). After a while everything seems fine - all photos are available with thumbnails in the events view. However all Faces thumbnails are missing - all persons in the faces view are black boxes. I can see that all the faces tagging are intact - when clicking a person I can see all the tagged images as black boxes. When switching the little "Faces - Photos" control to "Photos" I can see the photos containing all the tagged persons all right. I seems like it's only the face thumbnails that are missing.
So far I have tried the following without succes:
Repaired the iPhoto database with iPhotos own tool (holding Command and Option down when starting iPhoto)
Updating the entire library from an earlier backup
Updated the faces database files from an earlier backup as explained in this post
I'm out of good ideas now - can anyone help?

Answer 1

Using iPhoto Library Manager  to Rebuild Your iPhoto Library
Download iPhoto Library Manager and launch.
Click on the Add Library button,                         
and select the library you want to add from those in the selection window.
Now that the library is listed in the left hand pane of iPLM, click on your library and go to the Library ➙ Rebuild Library menu option
In the next  window name the new library and select the location you want it to be placed.
Click on the Create button.
Note 1: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments. However, books, calendars, cards and slideshows will be lost.
Note 2:  Your current library will be left untouched for further attempts at a fix if so desired.
OT