@ed3vlin, rwross,
Typical of Apple, I'm tempted to say. Two Apple support reps tell ed3vlin that restoring 9.1.1 from Time Machine seems to be the best work around, while Apple Engineering warns against this, unless one rebuilds the iPhoto library!
After reading ed3vlin's "all clear" I restored 9.1.1 from Time Machine and synchronized my iPhone and iPad. After reading rwross' contribution I rebuilt the iPhoto library "just to be sure" (because everything seemed to be OK, as others who have restored 9.1.1 report), only to have the places assigned to my photos -- I can't say whether all or only the ones I randomly sampled -- disappear! A pin appears on the tiny map, but instead of a place name the prompt to specify a place appears. So now I'm restoring the version of the iPhoto library that was current as of iPhoto 9.1.1 and crossing my fingers. If everything goes well, I'll only have to redo a few things. And, if not, I guess I'll have to redo the 9.1.2 update and restore the version the the iPhoto library that was current before I restored 9.1.1.
This is really absurd.