I am having the same problem with footage coming from a Canon HF-S100. FCP interpretates it wrong, labeling it with "none" as a field order. I am using the following walk around: in the browser, I set the clips to the correct "upper" before I drag them on the sequence. Just to make sure I did not forget anything, before delivering I select all the video in the sequence (no audio), check item properties (from the timeline, not the browser) and correct files that may be wrong. Then I export a video clip with the proves settings, and place it into a sequence with the master tape settings (HDV or DV). I am now sure everything is fine. Conforming to sequence will cause a zoom in is the clip is HD and the timeline is SD, so I find it best not to copy and paste the sequence's clips in the new timeline, but the file I exported. Hope this helps.
Sorry, I don't know how but a previous post showed here with a wrong subject. Here is the correct text:
I made a search before posting, but if I'm not wrong there's no previous post about the announcement of a beta driver from Blackmagic that will allow real time external monitoring with FCP X: http://www.blackmagic-design.com/press/pressdetails/?releaseID=26930