This is actually works differently when at phab.enlightenment.org and on secure.phabricator.com

phab.enlightenment.org

1. Create a page in phriction (with a / or | in the title of that page.
2. Create a Task in maniphest
3. Attempt to link to that page you made...

Result : When I tried to link to this Arcanist and Review | Submission, remark ends up making the title Submission, and the link it generates points towards a nonexistent page.

secure.phabricator.com

1. Create a page in phriction (with a / or | in the title of that page.
2. Create a Task in maniphest
3. Attempt to link to that page you made...

Result : When I tried to link to my Test Page | wPipe on here, remark up ends up making the wPipe and links to this : https://secure.phabricator.com/w/test_page/

Example : wPipe

Example at phab.enlightenment.org - You'll have to test it to reproduce it.