iphoto is trying to reorganise pics

[maenad]

Apologies if this is in the wrong branch - I can't seem to find a post dedicated to iphotos.

I've got iphoto version 8-1-2. It's always been tough to use (duplicates drive me nuts) but has never tried this before -

I downloaded some holiday photos last summer and put them all together in one "event."
I occasionally looked at them after that.
My ancient father-in-law poked my computer a few times while looking at family pics. That was a week ago. (Don't know if he did anything).

Now I find that about half my events - not all - have been divided day-by-day. I don't want that. Is this due to an update or something?