What's up with Harry's Scarf?

I forgot to mention that I noticed in the 4th Harry Potter movie his scarf has changed patterns. Maybe they switched it in the last movie and I didn't notice. (I've searched all over the web and there doesn't seem to be an image of Harry from the 3rd movie with the scarf on so I can't really say.) Anyway, I noticed this right away because being the crafty person that I am, I've already made a couple of the scarves according to the first pattern. So why did they go and change it? To keep Harry hip and modern? To make every little kid demand the new patterned scarf for Christmas? To make crafty people like us go nuts until they run out, buy the yarn and make the new patterned scarf as quickly as possible? I'll let you know my feelings on the subject as soon as I get back from the yarn shop.