See the very informative original report: https://en.wikipedia.org/w/index.php?oldid=864094427#Unable_to_publish_a_very_specific_change_(an_AfD_page)_at_any_namespace_as_an_unregistered_contributor
Steps to reproduce:
- Log out or use non-autoconfirmed account at the English Wikipedia.
- Put this on a page (including an existing page):
- Try to save the page.
This should trigger a CAPTCHA, but it doesn't. And since you can't enter the CAPTCHA, you can't save the page.