Pasting an image into a comment also uploads design

Summary

Pasting into a comment form on an issue also uploads a design.

Steps to reproduce

1. Copy an image into the clipboard.
2. Paste it into a comment form using Ctrl-v

What is the current bug behavior?

The image is both uploaded as an attachment and inserted into the Markdown, and also uploaded as a design.

What is the expected correct behavior?

The image should only be added to the comment form.

Output of checks

This bug happens on GitLab.com

Possible fixes