This bug's been driving us mad because we can't reliably repro it on our machines at Docker, and it only happens to a small subset of users, but is very annoying when it goes trigger. It seems to be related to the OSX version involved, but there's not enough bug reports to reliably hone in on it.
The other aspect that it may be is a long-running Docker.app -- since as developers we are frequently killing and restarting the application, it could happen after a period of time. I've now got two laptops that I work on, and one of them has no Homebrew or developer tools installed outside of containers, and runs the stable version of Docker.app that's just been released. If this can trigger the bug, we will hunt it down and fix it :-) In the meanwhile, if anyone can trigger it and get a backtrace of the com.docker process, that would be most helpful. Bug reports can go on https://github.com/docker/for-mac/issues
