I'm having problems with the clips I speeded up. When I render them or I exports the sequence they loose the sync and right cut. It does not take the exact portion of the clip I had selected.
What could be the problem?
would help to know what version of FCP and your sequence settings.
Most such issues can be resolved by working around them. Place your clip into an empty sequence, adjust the speed, render, export the rendered sequence as a self-contained movie, import.