Every time I tag a bunch of faces and click "Done", iPhoto starts to rescan all the photos with uncomfirmed faces.
I assume this is happening because CPU usage by iPhoto jumps to ~99% and all the probably matches for each person disappear. I also see the spinning "busy" icon in the possible matches sections at this point.
Is that indeed what is occurring? If so, how can I stop it from redoing the scan? It's kind of inconvenient because I have ~10k photos and all the suggested face matches can go away after I only tag 20 photos or so.