This has bothered me for quite awhile and makes no sense to me what-so-ever.
We'll just go by what's canon and not what's in the movie (but in the movie, he's a seeker).
So, in OotP James is playing around with the snitch, then JKR goes and does an interview saying James is a chaser.
Why would a chaser be playing around with a snitch? Do you think Katie Bell would do this? Angelina? Alicia? Even Roger Davies? No, I don't. However, Harry is seen doing this, in a less pompous way, in OotP.
I know James is a show off, but come one, show off with your own position so you don't seem like even more of a butt.
Personally, I see this as JKR messing up in an interview and refusing to admit it, or changing her mind (ahem, the number of students switching from hundreds to thousands). I know she has creative control, but she needs to stick to what she's already said and stop changing things!
END RANT.