I’ve seen this a lot with PPro. It has something to do with the importer. C300 uses spanned clips, so there are 4 files in your 20 min. clip. FCP X interprets this correctly as one single file. PPro seems to bring in the 4 component files, but then each one duplicates the other pieces, resulting in 4 x 20 min. clips. This behavior might vary if the files are on a network or local.
Oliver Peters Post Production Services, LLC