Picture - Audio sync adds frames

I've recently transitioned from FCP7 to FCPX and am completely bamboozled by an audio sync issue I'm having.

I'm working as part of feature film workflow which includes R3d footage and separate audio. This separate audio is often longer than the picture clip, when the sound recordist has hit record before the camera guys.

The problem with this is that FCPX adds black frames at the start of the new syncronised compound clip, in order to preserve the full audio clip.

This would normally be fine, merged clips do the same in FCP7 - HOWEVER, because of our particular workflow, we have to go back to FCP7 which involves stripping the compound clips and converting the fcpxml to xml. During this process, the clips are given new in/out points due to their new start frames (black added at the beginning).

This is causing havoc when conforming to raw rushes/R3d files, basically they don't match up.

Has anyone else had this issue/found a workaround?

Thanks in advance

SSsooo... you're using FCP X to sync clips, but editing them in 7? I'm confused about your workflow. Once synced, why not export as a QT .mov and bake it in? You can also open that sync'ed clip (simply a compound clip) into it's own timeline and trim the black out?