Larry,
hi, me again. I'm not here to argue. I've been an Apple devotee since the 80's, currently have 3 Macs, an iPhone, iPad and Apple TV. I've sung Apple's praises long and hard (though the recent dumbing-down of some mac apps has taken a little of the shine off for me). When I posted a few weeks ago I was annoyed, having been working on a photo that would't hold its edits. Again. Normally I don't bash Apple.
This is an old thread and a long one, but you should read it. I know you haven't because, in the light of it, your statements here appear foolish. Briefly: unable to fix this problem, the Original Poster left his computer at an Apple Genius Bar where it was reformatted and everything reinstalled from scratch. The Genius then reproduced the problem. He then copied one of the OP's photos to the store computer and reproduced the problem there. At this point he rightly told the OP that the problem wasn't fixable. That's why I know not to accept your offer to troubleshoot. I've done plenty of it but, from the preceding, I know pushing on is futile.
It's great (for you) that this problem hasn't manifested for you. I don't know enough to hazard a guess at what's going wrong, but I think there's a clue in this thread: one poster has two photos of a landmark, taken at the same time, one of which displays the problem and one that doesn't. There's a clue in there somewhere ...
You can't claim there is no problem in iPhoto until you can reliably edit a photo that someone else can't. And, as the Apple Genius demonstrated, that's not possible. If the problem exists, it's unfixable. And, from the number of unrelated posters in this thread, I think it's fair to say the problem is widespread.
I daresay Apple gave up on this a long time ago, knowing that they were ditching iPhoto for the new Photos app in Yosemite. That will be out soon and, hopefully, this problem will disappear.
Steve = : ^ )