Why does this project generate infinite previews upon rendering?

Summary:

I have a sequence with three video tracks and one discrete audio track, all synced. If I change the order of the video tracks and hit "render in to out," the rendering never stops because new previews are continually added to the rendering queue!

Details:

I'm working on a three-camera project. Key steps so far:

- Placed 17 clips from the three cams onto three video tracks and synced them.

- Added a discrete audio track and synced it, then deleted the other audio tracks.

- Moved the discrete audio track up the the "A1" position.

- Began rough cutting the three video tracks.

I soon saw that cutting would go better with the primary camera stacked on top, in the "V3" position, not on the bottom in the "V1" position. So I simply selected all of V1, dragged it above V3, being careful to snap it into place to keep the sync. Then I deleted the now-empty V1 track, moving all three tracks down one position.

I hit "Render In To Out" before attempting to save the new track arrangement. The rendering window popped up, showing 17 previews to be rendered. So far, so good.

I walked away, came back an hour later, and the render window said "Rendering 137 of 137 previews"!! And the number was increasing by the second! The green progress bar was pinned at "99.32% completed" and would go no farther.

I let it run another 20 minutes and the render window said "Rendering 304 of 304 previews" or something, the number still climbing.

So I canceled the operation. I sketched up a similar project to experiment with. Whenever I tried the same maneuver -- moving a video track to a higher position -- I got the same problem.

I could just start this project over with the cams in the right order, but that would be a pain. Besides, I'd like to know why this isn't working, for future reference.

Thanks for your time.