Originally, I think the price rise was due Jan 1st. It has since been delayed to Feb 1. Haven't been able to clear up if the cut-off point is the manufacturing date or delivery date but if your car is built after Feb 1st, the price rise will be passed onto you.
I agree about this being a bit hard to swallow but it is not something new. The difficulty here is that due to the waiting list on some models, the chances of this happening are greatly increased. Happy to hear if anyone knows the details that allow car manufacturers to get away with this but it looks as though we're put in this position simply because of the popularity of the car. I would have thought a fairer system would be to make the price increase from an order date rather than delivery date.
To make matters worse, I've heard that another increase mid year will occur. Basically, if you order for example an XR6T in late Jan, you could potentially be faced with 2 increases considering the waiting list.