Confirmed.
It was exactly the problem.
I don’t know how to fix it, so I just describe other ways:
Each time after the javascript pop-up runs, then the content field is gone.
You won’t be able to see it again either with admin or editor role.
You have to disable-reload the mm-plugin.
Ok, this time another bug report:
In editor role, if I made a content with Editor role, then the Site Tree icons were missing.

But after it’d been edited again by admin role, the icons showed up (in the example pic: test again (3)).