thanks for your help.
Actually, i get this issue in both the viewer and canvas.
Yes, clip settings match the sequence settings.
Tried with prores LT, and regular prores 422. same problem.
Been editing for 10 years, never saw something like this before. I was suspecting Mavericks, but makes no sense as i did some jobs with Mavericks insatlled, and fcp7 worked fine.
Thanks for help, if you have any ideas.