I think the recent sale ($339) is to get rid of remaining s-ips stock before the new cheaper 20" comes out, then I suspect that after the panel switch is complete and hits USA, the 'new' 2007WFP will remain at a ~350ish price to distinguish a difference between it and the new model.
Also, there is a chance that there is no switch. Maybe they just had a shortage on panels and used some other one overseas for awhile ? Seems unlikely, but so does a stealth switch in panels... I mean, why not change the part number then to a 2008WFP and call it 'improved' ?