The Grand Master's effect only applies if the instant or sorcery would go to the graveyard while it's resolving. Temportal Trespass won't try to go to the graveyard, however - it exiles itself as part of resolving. Since it never tries to go to the graveyard, it cannot be returned to your hand and it ends up exiled.
We're treating all face-down permanents and spells the same way. It doesn't matter if it was manifested or cast via morph - when the game ends (or if the face down card would leave the battlefield or the face down spell would leave the stack except to go to the battlefield), it must be revealed to all players. And remember: not revealing the face down card at the end of the game is a warning now, it's no longer a game loss. Manifest doesn't change this.
Nathan Long
Wizards.Com Boards NetRep