This bug comes from time to time and I finally took a screenshot to report it. Pity that for some reason the screenshot was cut, but serves as proof anyway.
I am not sure how to replicate this. The sequence of steps is the same, but as far as I am aware it doesn't happen always.
- Edit a page (I was editing with VisualEditor-MediaWiki-2017WikitextEditor and this is why I am adding the tag just in case).
- Save changes normally. Check that you are in a "read" mode again.
- Introduce another URL in the browser, press Enter.
The dialog appears.
This happened with Chromium Version 55.0.2883.75 built on Debian stretch/sid, running on Debian 9.0 (64-bit). The diff, just in case it is useful.