"Comment & close merge request" not working (only closes but does not comment)

Summary

It seems the "Comment & close merge request" button in merge requests is broken.

I'm not sure if it happens every time but I noticed at least two times now that when clicking this button the merge request is closed but the comment never added.

Example Project

I just tried to close inkscape/inkscape!63 (closed)

The MR was closed, but the comment was not added (I had to "comment" again in a separate second step)

(I'm using Firefox 54.0.1 on Windows 10 in case this is a client-side issue)