I was able to reproduce this for images that were inserted using quick-reply or quick-edit during the same page load (the image was not actually in the post before the edit/reply, after posting the image would "load" indefinitely, and reloading the page would load the image successfully). This is fixed in the next release.
The issue also affected the wiki's GALLERY tag, the multi-page option of the wiki's WIDGET tag, the wiki's sortable TABLEs, and possibly other variations of some tags.