PsF clip "converted" to Progressive in Inspector needs rendering in Progressive Project?

My Panasonic SD800, likeall AVCHD cams, shoots Progressive as PsF.

FCP X incorrectly recognises it as 1080i so I opened the Settings View and selectedField Dominance Override: Progressive.

The Basic and Extended Views still had it listed as 1080i until I quit and rlaunched FCP X.

I then created a Progressive project and put the clip in whereupon a brown rendering line appeared above and took over twice the time of the clip to render. (A new Mac would do it in less time than the length of the clip).

The same thing occurred when I created a new project and set its Video Properties to be based on the first video clip.

So why does a progressive clip need rendering when placed in a progressive project? (I am using the clip natively as AVCHD/H.264)

Incidentally, I am no more impressed with progressive than I was 4 years ago.

I cannot see any quality benefits but do notice an irritating jitter on motion.

Probably if I stuck to making videos of stills it would be satifactory but video cameras are made for filming movement!