In this situation, actually the final version is "correct". There is a set of (currently hard coded) criteria that determines whether someone gets their links nofollow'd. However, the default state in the BB code parser is to nofollow things.
The preview doesn't respect the isTrusted option, but the regular thread view does.
However, if can be a pain to set all this up and as the preview is transient (making the property not matter), it's not worth changing.