The Incubator extension doesn't prevent editing in Category & Category talk for prefixed pages which belong to an existing subdomain (as it does in the other NSes).
Very strange. I don't remember on which page I noticed it yesterday (I deleted 3 ex-test-projects, in one of them I saw it). Restoring a page also can't reproduce it.
We can see whether it occurs again when a new subdomain is created.
Solution: It works correctly, except for the main category:
https://incubator.wikimedia.org/w/index.php?title=Category:Wp/olo&action=edit can be edited
https://incubator.wikimedia.org/w/index.php?title=Category:Wp/olo/Filosoufii&action=edit cannot be edited
That's because you have the editinterface right. The Incubator extension allows users with the editinterface right to edit any main pages for each test wiki. Try it when logged out and you would not be able to edit the page. Do you suggest that these pages should not be edited?