I have just come across this when reviewing this question:
- Original post contained an image
- Answer, by the OP, also contained an image, which was adding more information to the question
- It was flagged by another users as not-an-answer
- As Mod, I converted it to an edit on the question
- Both the original image and the newly added images had  in the tags - this meant that the new image was incorrectly displayed twice.
- I then had to perform a subsequent edit to fix the tags for the second image so that both displayed correctly.
Can the last step be done automatically as part of the merge process?