We're running 2.8.2 with a master and 10 child processes, each running 4 threads. We got into a really strange state where there was only 2 children running because the master was somehow running out of file descriptors so it couldn't start any more children.

I'd suggest this case should result in the master process exiting completely. If it had, upstart would have restarted the master and everything would have gone back to normal.