I am referring to this discussion https://moodle.org/mod/forum/discuss.php?d=354672#p1430749 which, unfortunately has been closed but the bug not fixed.
From what I understand, this is what happens to a random short-answer question built from short-answer questions containing an image. The reference to the image(s) is indeed there, but there is one "item" in the image reference that gets increased each time the question is displayed. And of course that reference does not correspond to the reference of the original image in the short-answer question. The item is the one I've put in bold in this reference (1424).
<img src="http://mymoodlesite/moodle/pluginfile.php/21/question/questiontext/1424/1/208/french%20flag.jpg" etc.
By the way, I disagree with this forum policy of closing discussions so soon. IMHO one year without new posts in a discussion is a very short space of time.