Dudely

I can't seem to make the changes "stick". I can move the selection just fine... but... how do you "lock it in" ? Enter simply deselects the area, as does ESC, leaving the image exactly as it was in the first place. I've tried clicking on it, doubleclicking, selecting other "modes", just about everything I could think of and yet I can't make the change permanent. Is this a bug or am I missing something? The help file doesn't say anything about this. Thank you