Most people I've spoken to on this matter believe that this is about generating your trajectory for the purpose of AROs, and that this movement up and down, while exists, is still free in terms of MOV.
I took that as the movement is free, however for the purpose of checking possible AROs you bump the Silhouette up and down as you go over the obstacle. You don't actually add measurement for the vault movement up/down.
To be honest, the wording for this rule is not very clear, assuming the FAQ entry. And having this discrepancy (you don't include the up and down movement when you measure movement distance, but you have to assume the model moving this way for ARO checks) doesn't help either. I am also quite confused by the fact that you have to measure every other kind of non-linear movement such as jumps -- the rules literally ask you to measure the trajectory: So I'm not entirely sure that you are not supposed to do this when vaulting. @ijw ?
You do exactly as the General Movement Rules and FAQ tell you to - the obstacle doesn't affect your movement at all, with the sole exception of the Silhouette moving up and down for LoF.
