Exact same problem- and I have the following
Ever since I have upgraded to iPhoto 11 I have discovered the following bug which is a right pain.
I take a photo with my Nikon at 3008 x 2000 pixels. I put this photo into iPhoto. Using command-I I pull up the metadata window. Many times when I double click on the thumbnail the photo opens and immediately zooms to some ridiculous size. A quick check in the Metadata window shows the reolution is no longer 3008 x 2000 but has changed to something like 1400x916. Huh? Duplicating that photo and then deleting the original - everything goes back to normal. Shut the computer down and re-open and guess what? now there's a bunch more photos with the exact same problem. Some people have suggested rebuilding the thumbnails but come on guys - even after doing this random photos fall foul of this bug. If it was just one or two I could perhaps live with it - but I've just had to correct over 200 photos. Tedious or what?
And don't get me started on cropping in an external editor. That's just a nightmare. I've had to resort to cropping my photos first in iPhoto to prevent iPhoto "stetching" externally cropped photos to fit. That seems to work. This is undoubtedly the buggiest version of iPhoto that I'ver ever used. It absolutely needs fixing.
And yes I have used the iPhoto feedback feature to complain to Apple about this.