I have a FCP sequence made of a mixture of ProRes 422 and PAL clips. As soon as I export it using "QuickTime Movie" (Apple ProRes 422 PAL 48KHz option), the quality of the ProRes clips is superb, but the PAL section look horrible (they look fine in the timeline). The same happens for the transitions effects, even if the transitions are between two ProRes clips. During the transitions, the quality of the exported movie drops dramatically.
What could be the issue?