cropping--wrong aspect ratio problem

for the past few months I have noticed strange things. I have an iMac 4GRAM (3 years old), using Aperture 3 with latest updates, etc. My library is quite large.

Problem #1: many times the program gives me a wrong crop aspect ratio by itself.

#2: some pictures becomes unrecognizable--filled with multiple tiny tiles ("pixelleted look"). Sometimes this happens when I try to crop the photo.

#3: some versions look ok on the computer but after uploading to Facebook or Flickr, the crop ratio is wrong. (ie. people's head are cut off. etc)

Any one know why this is happening? what's the fix? When I creat a new version from master, I do not see these cropping issues.

Thanks for much in advance.