It was discovered that in some cases a build in a docker container would cause the container to terminate.  It appeared that the mini init program in the container would simply exist.

In a heavily loaded container, the child process might not started before the parent process had terminated.  The child process attempts to signal the parent with SIGUSR1.  If the parent had terminated, the parent becomes PID 1, which is generally init.  When it signaled pid 1, it caused the docker mini-init to terminate.

This doesn't happen in a traditional system, as systemd/sysvinit is protected to only root users can signal it.

This was fixed in the pseudo commit: 647ea4b1bc780b40a852e7e2d1439f700339e613