When saving a comment failed, the comment is lost

Steps to (sometimes) reproduce:

• In the diff view of an MR, write a comment.
• Let's say saving that comment fails for some reason.

Now the comment text is lost! I just had to write the same comment text 3 times due to this bug. This is one of the worst kinds of bugs since it loses data.

What should happen instead is that the text field where I typed the comment stays open, so that I can copy-paste the text and e.g. try again in a new tab. The text field should only be removed once its content has been successfully stored on the server.