Create a page with the following wikitext external link:
[https://phabricator.wikimedia.org/maniphest/task/create/?title=[REQUEST] create a task]
(this is a Phabricator link which opens the task creation form with a prepopulated title).

It renders properly in the read view, but when you open it in the visual editor, it simply renders as the text [https://phabricator.wikimedia.org/maniphest/task/create/?title=[REQUEST] create a task].

There is no problem when you use percent-encoding instead of character entity references in the URL: [https://phabricator.wikimedia.org/maniphest/task/create/?title=%5BREQUEST%5D create a task]