I found a quite big bug here. When using the image editor of a sprite and changing an image it won't update and save, but rather revert to it's previous state.
I've made a link to an easy example here:
This can be done by the following steps:
Open the image editor of the sprite (1 = green, 2 = red, 3 = yellow). Select the second or third frame (red or yellow) and load a new image (eg yellow or green). It will update in the image editor as it should, but as soon as you either close the image editor or click on another frame (or animation), it reverts back to the previous image again. The only solution I found for this is to remove all frames and start over from scratch again.
Windows 7 Home Premium 64-bit