When you click the pencil icon in the Maniphest task list, we currently fatal:
Argument 1 passed to PhabricatorCustomFieldList::appendFieldsToForm() must be an instance of AphrontFormView, instance of PHUIFormLayoutView given, called in /core/lib/phabricator/src/applications/maniphest/controller/ManiphestTaskEditController.php on line 576 and defined
This is because we build an AphrontFormView noramlly, but a PHUIFormLayoutView for dialogs, since they don't take a full form (they render their own form tag).
Instead, always build an AphrontFormView and just pull the PHUIFormLayoutView out of it when we're ready to put it in a dialog. This means $form is always the same type of object, and is generally better and makes more sense.