I'm having an issue where a gallery's preview image seems to revert to "no image" by itself. I've seen it happen randomly, and the same steps I take to duplicate the problem will not always reproduce the problem. Here is my workflow:
--I change some property of the gallery or images inside the gallery.
--leave the gallery
--go back into the gallery.
--The image that was selected as the preview image is now set to "no picture".
I using 1.5.3 with NextGen Custom Fields 1.0.2