The basic issue is that when I was recording (rendering a MIDI track to audio), the displayed soundbite out paced the timeline. The longer I recorded, the farther ahead it got. When I stopped recording, the (displayed) soundbite was significantly shorter than the actual data. If I played it, it played through to the end of the recording (but beyond the soundbite edge) as expected. If I tried to edge-edit the soundbite so I could see it, I got the circle-slash cursor. If I switched to the trim tool, it acted even more bizarre.
I've written a tech-link on it FWIW.
