That's new info for me. I'm not sure how I ended up with the notion that SP locks in, but thanks for clearing that up. I've wasted many GCDs applying a new SW:P to that end.
New info? It's been like that ever since our WOTLK talents were released, same goes for crit back when it was a %-increase of dot damage. How you can miss things like that is beyond me.
On topic, I find the crit lock-in very annoying especially on fights with any kind of target swapping where we want SWPain up as fast as possible to boost MB and MF.
Another question, what classes do you see benefitting most from buffs such as Power Infusion and Focus Magic (after mages). On single-target fights and multi-dot fights? A well-timed Power Infusion on a priest when a new wave of adds spawn or when we can Mind Sear I don't see ANY other class beating us in terms of benefits from PI, not even mages.