[spoiler]so, when barnabas discovered why quentin was cursed, he should have gone back in time to prevent quentin from killing jenny racosi collins, thereby avoiding the curse.[/spoiler]
[spoiler]And since Trask had been trapped in there with Quentin's exstensive library of books on black magic, do you think Trask's spirit might have perused those books throughout the decades and learned a thing or two? Who knows, maybe Trask, wanting revenge on the Collins family, conjured up Quentin & Beth's spirits from the grave , took control of them & forced them to do his bidding by haunting Collinwood.[/spoiler]
later on however it's never quite satisfactorily explained as to why everyone readily accepts quentin into the household and no longer equate him with the ghost that caused them so much grief.
Another idea I've seen used to explain the differnence in the ghost is that it's the ghost of PETOFI IN QUENTINS BODY. He, at least had the perquisite evil sense of humor....
Clearly he's solid and not a ghost, so they can't say otherwise.
You're right about Petofi not having been around originally -- or at least the best we can TELL,with the cats cradle Barn made of the original timeline.