Kosta and Cindy reported this to me in the last days when they wanted to edit a (sub)task someone else had filed:
When selecting "Edit related tasks" and then "Create subtask", those tasks were set to "Can Edit: Task author, Administrators, WMF-NDA". There are no signs of policy changes in the log so it looks like this policy was set on task creation.
The subtask author did not get the fields "Visible To" and "Editable By" when editing the subtasks.
This seems to confuse [some] people. I've received messages by four people (WMF, WMDE) so far who wondered what's wrong and 'how to get rights'.
(This does not mean that we should revert this change completely but that we'll probably need to adjust the criteria or how to add people automagically. Somehow.)
I can confirm this is not only confusing but *really* annoying and disturbing in daily work on Phabricator. To be honest I personally can't see any reason why this should be useful in any way, but even if some projects may want this, there's no reason to force this on all of them and effectively making collaborating impossible in huge parts of Phabricator.
This should be resolved now: I changed default edit policy on maniphest tasks back to "all users" until a better solution can be found.
For the records, this creates confusion such as https://www.mediawiki.org/wiki/Topic:Ukx06nfuevy32fqo
I went through remaining open tasks which have open parent tasks filed between 20180710 and 20180731 and reset the Edit Policy to All Users for those tasks in S1 with View Policy set to Public.