Changing date (and sequence) of events by changing dates of photos no longer seems to work. Any idea what to do?

Question

I am scanning in old slides and negatives (from the 1960s and 70s), and I want to get the resulting "events" in sequence from when the photos were taken, rather than when they were scanned. So I have been changing the dates of the photos, and previously this resulted in the associated event moving to the proper sequence. This definitely worked a month or so ago, both with prints scanned in on a flat-bed scanner, and also with slides and negatives scanned with a Veho scanner. That was faulty, however, and so it has been replaced with a Plustek 7500i scanner, using SilverFast scanning software, and importing the resulting images into iPhoto. I have recently tried to change the dates of the resulting events, and it doesn't seem to work as it used to. There has been an update to iPhoto 9.1.3 since my earlier success.
Take for example one event, CS73A. Hovering over the event in the "All events" display gives dates of 1 Apr 2011 to 2 Apr 2011; these are the dates the slides were scanned in. If I open the event and choose the Info tab, it gives the event date as 02/03/1973 (which is the approximate date that I changed it to). I had done a batch change on the event this time, so the date and time on the first slide is 2 March 1973 09:30:48. Each successive slide is 1 minute later, and the last is 2 March 1973 10:08:48 (38 slides). I asked for the dates in the files to be changed as well.
I don't know what I'm doing that's different from before. The only things I can think of are (a) something has changed in the iPhoto update, or (b) the SilverFast software stores the scanning date in some part of the EXIF that iPhoto can read but not change. I don't have tools to examine the EXIF unfortunately.
What to do?

Answer 1

Chris, I have run into the same problem.
Try this:
Open an event with more than one photo in it.
Adjust the date of one or more photos. The event date does not update.
Delete any one photo. The event date now updates to match the above date change.
Undo the delete photo. The event date stays matching.
Change the date of any photo again. The event date updates now every time.
If you close the event and reopen it, you have to start over with the delete one photo thing.
I don't understand it but it works here.
I also have had the problem of events not sorting themselves in order of the dates when VIEW, SORT, BY DATE is selected. This seems to affect only the events were photo date changes had been made. Using the delete thing seems to keep the events in order.
Another funny thing: When I put photos into iMovie the times in iMovie show as 7 hours off the photo time.
I think Apple owes us an update to iLife!