You also may be getting the double-anamorphic effect that comes from changing anamorphic settings of a sequence after anamorphic clips are already in (and other such scenarios where FCP's behavior is based on relative rather than fixed changes). For this, their solution would be to manually change the aspect ratio if the clips in the motion tab, match frame and reedit the clips, or (as long as there isn't any other basic motion stuff going on) just change one clip and copy-paste basic motion attributes to the rest. This doesn't help you now of course - what the people delivering the material really need to do is edit anamorphic in an anamorphic sequence from the get go, then if they want letterboxed they can nest it into into a 4:3 sequence (or deliver 16:9 to you leaving you with all the options).
Brook _______________________________________________________ Brook Hinton film/video/audio art www.brookhinton.com studio vlog/blog: www.brookhinton.com/temporalab [Non-text portions of this message have been removed]