Was just about to post this issue as well. Ditto, and I really need this functionality to work.
Also, when you link a dynamic image the toolbar shows a generic background image, not the dynamically linked image – not a show-stopper, but the visual feedback is off-putting the first time someone might learn and use the feature.
Never mind (for now, at least). The work-around is to attach a Div. to the Section that’s absolute positioned, is same height, etc. (as if you were creating an interactive overlay); add a gradient to the div; done.