I'll try and explain the best I can...
I'm working with Elements 3.0. For this example, I'm using only two still images (jpeg). One as a background, one with a figure surrounded by green, which I eliminate with the green screen key.
I have the figure in front gradually increase in size using motion.
Now, with the 'figure' motion keys in place, I drop the green screen key on it, and as soon as I make a setting change, 'poof', the image (figure) is a good 200% larger than it should be (Im guessing, it's huge and rather random). Rendering doesn't help to get rid of whatever glitch this is.
If I adjust the motion even slightly, it immediately shrinks to the proper size...but only on that particular frame. The rest of the famess are still bloated.
I've had the same issue with a movie clip, but am currently working only with stills. It very much 'seems' to be related to the color keys, but I've no clue why? Or how to fix it. Very frustrating.
I don't recall any such issue with 2.0, though I 'could' be mistaken. I fully uninstalled that before "upgrading" (kinda wish I hadnt now). Any ideas would be greatly appreciated!