persisting something under /etc breaks the system

[damscal]

I'm on nixos-unstable.
Whenever I try to persist a directory under /etc, such as with:

environment.persistence = {
    "/persist" = {
      directories = ["/etc/test"];
    };
  };

On nixos-rebuild switch I get:

Error: Failed to restart nixos-activation.service

Caused by:
    Unit nixos-activation.service not found.
restarting sysinit-reactivation.target
the following new units were started: etc-test.mount, libvirtd.service, system-systemd\x2dcoredump.slice
warning: the following units failed: nginx-config-reload.service

The mount of /etc/test is successful, but the system looses internet access.
At shutdown the process hangs for 1min 49s with the message:
A stop job is running for User Manager for UID 1000 (23s / 1min 49s)

The system ultimately fails to reboot with the error:
Failed to start message bus: Failed to open "/etc/dbus-1/session.conf": Permission denied
In addition to a bunch of services failing to start.
I also tried using nixos-rebuild boot with the same result.