I've heard tales of plug-ins and effects processes doing bad things to the spatial perception of a soundfield. Of course, most of those tales come out of the music industry, where a mastering engineer has to restore or widen the stereo image because it has completely collapsed after an inexperienced mixing engineer has slapped some plugin(s) on the master output bus (the most common offeneder listed is a compressor).
It's been a while since I worked heavily in music, and most people in our line of work aren't usually throwing global processes onto our mixes, so I haven't ever encountered this. Has anyone had this issue when working on a film/tv mix? If so, what were the circumstances.