I make the round trip to LR exactly as you describe except that I have PSE set to prompt me to overwrite the existing file. It always prompts and I always choose Yes so I know I am over writing the the file. I also know I am over writing the file because after returning to LR I can view the photo at 1:1, which forces creation of a new preview, and I then see the changes made in PSE.
So, back to my original question. Is there any way to force LR to regenerate the preview for a single image or for all of the image in a folder?
