There’s an open ticket but we can’t get any closure on it. I actually see this in a controller on a production 1.2.3 app occasionally. It’s quite irritating.
See here for a good start:
Perhaps if the related ticket at http://dev.rubyonrails.org/ticket/7452 gets some more attention, this bug will too. The problem is that we don’t get much attention to bugs from the core unless we can show how to reproduce the problem, which I totally understand… but this one’s a bit difficult to track down or reproduce on demand.
In my case, I bounce the system and I’m good, but apps stopping really stink.