I have been getting this issue since this morning, I think this has something to do with changing image size when the size of an image gets adjusted or changed.
I do not have the exact steps to reproduce for now.But it happened this one time when I changed the thumbnail left aligned image to centre float.
This is the page where you will see the image on which I made the change and getting the edit conflict error :
We had encountered similar kind of issue quiet a while ago, which was fixed:
I am not sure, if the same cause is behind the bug or not