Steps to reproduce:

1. Set prefs to use 2017WTE
2. Click "New section" to open the New Discussion tool.
3. See the "hint".
4. Click link to switch to the legacy experience (i.e., the 2017 wikitext editor).
5. The hint is now inside one of VisualEditor's alert boxes. Click the link to "return to the new experience".
6. Discover that returning to the new experience opens the New Discussion tool opens the page in a new tab. Now you have two tabs open for the same section.