Thanks for the response. I actually found that when I used anamorphic settings, the video looked very stretched out, as though I was using those settings on a 4:3 clip (Sanguinity also seems to have had this or a similar problem downthread), though I switched the aspect ratio to 16:9 in the "options" button in Streamclip. So even when using 16:9 I end up using 4:3 settings in FCP, and I think that might be where the non-square pixels somehow become an issue? I talk about this a bit more in my response to Sanquinity.