Forum:Optional Trigger Effect Question

Alright I'm a little confused right now by one thing in particular. From what I have been discussing with other judges, they have told me that Optional Trigger Effects that start with "When" (ex. Dark Magician of Chaos, Peten the Dark Clown, etc.) can miss the timing whereas the ones that start with "If" (XX-Saber Darksoul, Scrap) cannot miss the timing. I understand why Darksoul works, but I'm mostly confused about the Scraps. For example, if my opponent plays MST on my facedown card, and I flip it to reveal Scrapstorm and use its effect on a Scrap Goblin, why wouldn't the Scrap Goblin miss the timing? So...
 * 1) Is that actually correct?
 * 2) If so, why?

Thanks! --Sub (Talk | Contribs) 21:50, September 2, 2010 (UTC)