Clips have turned red on the timeline in 9c

I have been working on a fairly simple two camera shoot in SV Pro 9c. Last night, I duplicated the two video tracks, moved them to the top of the stack, and muted the original tracks. I then selected the two duplicated tracks, and created a multicamera track.

Today, a video clip on one of the original tracks is displaying as a bright red color on the time line. Similarly, some of the video on the multicamera track is a bright red. Previously, all video tracks showed image thumbnails on the timeline. Everything seems to play normally although I have not attempted any renders.

What is the bright red color indicating? Should I move this project back to Pro 8 before spending more time on it?