I've recently upgraded from 10.6 to 10.7 and I'm having an issue with Preview. I've just opened some JPEGs, resized them (because the originals are huge), and used File > Export (which seems to have been renamed from Save As) to save the resized copies. However, the original files are now small too! It looks like Preview is automatically saving to the originals, because I didn't manually save them and it didn't prompt me to save when I quit Preview. I can't find anything in the preferences for this. How can I stop Preview from automatically saving?