I set up a multi-cam edit in the "normal" way. That is, I created nested sequences. First, my source sequence with two tracks of video/audio. Then my multi-cam edit sequence. Then I took the multi-cam edit sequence and nested it into several subset sequences (my producer wants several short web videos from this two-camera interview). Everything working more or less as you'd think it would. Edited out about half of the footage in my first subset sequence, then started to do a little light color grading using the three-way color correction video effect.
All this took of course is that I had to drag the three-way color corrector to the first clip on the timeline. Played with this a bit trying to get the clip to look like I wanted. Then I looked down and noticed that all my other sequences were "gone". The tabs for them read "timeline: (no sequences)" and when I clicked on the tab, there was nothing there -- no tracks, nothing to even drag a sequence down to. Big empty hole. No source sequence any more. No multi-cam edit sequence. Yet, the subset sequence I was working with is fine.
I must have done something to cause this --- but what? I'd like to know so I don't do it again.
How can I recover? I'd like to get those sequence back so I can change some things that will ripple down (or up?) to my nested subset sequence (third layer). Is this possible or am I just hosed?
Oy. Forgot to add that I'm using CS5, and created this project in CS5.
Oy again. Finally hit upon the correct search terms. Turns out this is a known bug in Premiere Pro, and has been hanging around unfixed since at least CS2. Unfixed because it's apparently fairly harmless. If I just delete the effected tabs, and double click on the sequence I'm interested in, it opens with a new timeline tab. All is well.
Sorry to have bothered those people who took the time to look.