Somehow, I think I've disabled the image editor.
It's been off for months now. (I thought it would become aparent to me in due course- but it hasn't.)
For example; If I create a new sprite object, click the paint bucket tool, select a color, and click the empty square: Nothing.
Can't use the other tools, either.
I can still import images, fine. But if I for example try to paint bucket tool an imported image- it acts like I selected the image and pressed delete.