Comment 14 for bug 494269

I think I have a handle on what is going on, and how to fix it. I just need to sort it through.

In brief, I think the code is set up to disallow 2 root ids, which is valid. However it does so too early. It should allow you to set up a new root, move everything into it, and delete the old root. At which time it can see that things are a no-op. And only at 'apply' time does it need to say "but you left 2 active roots, I cannot support that."