I tried to import a 4:3 HD video (960x720) in Prores LT format to FCPX but in the import window, the frame just got stretch to 16:9, and it kept that aspect ratio after importing. That problem does not happen when I import H.264 version of that video.
Does anyone know what happened to me and how to fix this?
Just found another funny thing: I used Compressor to convert that piece of video (the previous time I had used Quicktime 7), it also got stretched in the preview pane and Compressor did not even start converting after hitting Batch button.
I think that because the only format that matches those specs is DCVProHD (which is anamorphic 16:9), that X has decided that it must be 16:9. There are no 4:3 HD formats so it took its best guess. You can just scale back the X scale value in the inspector.