I have discovered that this happens if I have multiple windows open showing the iShop, or if I hit the BACK button to a prior layout. It was making me crazy; I'd carefully rearrange (which goes VERY fast now, using a two-button + scroll mouse!), close, and think I was set, but if I backtracked to another window, or used another tab which had the old iShop pattern up, and did anything there I was screwed. I'd accidentally override my new settings by doing something in the old image.
I suggest testing this: Make sure to work in a SINGLE window, then close out of your browser and reopen.
I hope this is relevant and helpful; it worked for me.