OK, it took two attempts to fix the post: first time, after removal of original image, I ended up with two copies, old (> 800px) and new (800px).
So I had to remove all images, save post w/o images at all, then edit it again. (And, again: this forum engine sucks, big time).
Now I have only one image, it's 800px, and it's still not inlined.
Ideas?