When I click "Flag for later" in a Maniphest task and add a note, this note is only visible at https://secure.phabricator.com/flag/, but not in the Maniphest task. It is also not shown when you click "Remove [Blue] Flag", but just silently deleted. As I typically use the note to remember the reason why I flagged this or that task and what I need to do with it, this makes the process more cumbersome than it needs to.
The note should be visible in the Maniphest UI, either around/"over" (as a tooltip) "Remove [Blue] Flag" on the top or perhaps directly above the comment input box.