How to reproduce:
1) Open an article and attach 2 (or more) images to it
2) Edit the images and add the following Numbers 1, 101, 102, etc...
3) Edit one of the textarea fields with WYSIWYG editor and add the images to the text... make sure you insert more than 1 image and one of them being the one with number 1 in between the others.
4) Save and re-load the page
Result: No all the images are presented, instead one of the images is displayed more than once
This happens only inside the editor. This issue doesn't affect the frontend but it's disturbing and confusing for the users.