I'm working with 1920 x 1080 transcoded footage from a 7D and 60D. The Easy Setup in FCP gives you a 1440 x 1080 sequence. Drop in the first clip and FCP asks if you want to conform to the footage. I'm thinking yes.
Second, FCP does not ask if you want to conform the footage, it should ask if you want FCP to change the seq. settings to match the media. Is your FCP different from all others?
The answer to number two above is most likely yes, if you want to edit without rendering every step of the way then idealy FCP should change the seq, settings so they match the media you're working with.