FCPX sync clips. What does it do to the ones it can't sync

Hello
I'm used to using Pluraleyes in FCP7 Which worked perfectly near the end. Pluraleyes would throw any clip that did not match into a red clip to show they were discarded.

X seems to pile them on top of each other down the timeline. Is this pretty well all that it will do when unmatchable clips are attempted?

Thank you,
Steve Marshall