I think I am getting to understand the Video Sequence Editor now but I see what seems like a bug with loading a DPX image. The image shows “wrapped around” so that about 15% of the right-hand side of the image is actually on the left. However, the very same image in TIFF format is framed correctly. Both images are 2048x1024 pixels in size. The problem occurs regardless of the project output dimensions (eg. 640x480, 1920x1080 or anything else).
My understanding from the below note was DPX is fully supported in version 2.42. Indeed they do load in “almost” correctly, the image is there, it is just shifted.
UPDATE: 1) the wrap-around amount depends on the DPX image size (relatively more offset on smaller files), and 2) there are a few garbage pixels in the very first line (upper left). The amount of the offset is about 256 pixels, which is maybe about 1k bytes depending on how the file actually stores the pixel data.
CONCLUSION: I believe the Blender DPX importer is misreading the DPX header size (thinking it is smaller than it actually is) so it starts displaying as image data what is actually part of the file header. This explains both observations above. This may not occur on all DPX files, but it is true on those written by Photoshop. Probably whoever wrote the importer was using sample DPX files from a different application that had a smaller header.
