Hi!. Today have tested the new built-in Cineform Codec and it export like a charm, very good in that sense...
I have looked carefully the exported file and found and strange "black halo" in a graphic that the original file don´t have (zoomed 400% and captured in the Premiere Timeline):

You can see clear that there IS a difference. I have exported in Quality 5, and tried the RGB+Alpha, and the results are the same!.
Playing the file at normal zoom I see that black shadow, and it disturb me because don´t want it...
Exporting in MOV with JPEG2000 codec don´t have any issues, so I think that is codec related.
Thanks!