When loading an image from url, if the image is the same as the original frame, ie the actual sprite animation frame (could be blank, or a generic picture, whatever) C3 will not overwrite the image and uses the last frame loaded from a url.
Took me a couple hours to figure this one out.
Finally figured it out by using the clear image data. The image that was different would override the image that mirrored the sprites actual image (but not vice versa). I fixed it by changing the color of the imported frame to where it was a shade darker than the actual animation frame and it works fine.
Worthy of a bug report or just work around it?