Currently, when editing a RAW using "edit in photoshop", there is no dialog box with options to choose from. Problem: One cannot choose whether the newly created image will be stacked with the original or not. And very confusing: Whether the image is stacked or not depends on how one has set this option *previously* (!) in an edit which shows the options dialog (e.g. edit a JPG, or edit with an external editor different from PS) - even if that edit was cancelled, which oddly enough makes it a workaround for setting this option.
So my idea is: When editing a RAW using "edit in photoshop", show a little dialog box containing only the option "stack with original". If I remember correctly, this was still the case in LR 1.x (the dialog box contained also the "what to edit", but fixed to "Edit a copy with LR adjustments", obviously).
P.S. I already sent that using the old bug report form a while ago (as a bug). I hope it's ok to re-post it here as an idea (so at least I can see whether I am the only one that misses this, or others like that idea, too).
There is now an option in Lightroom 4 beta's preferences, so you can decide whether to stack externally edited photos with original or not. You can learn more about the beta here: http://blogs.adobe.com/lightroomjourn...