There is probably a caching issue you can reproduce simply:

Add an image to an animation, make edits in the image itself (with a graphic tool), when you now choose the image again for refresh (or even delete it and create a new one pointing to the same source) this image is still the same and you do not see the changes you made; I assume this is some caching error.
I had to rename the image to be able to include the edited image.