Comment 2 for bug 1349635

Easier steps to reproduce this, without breaking your networking setup (hopefully):
1. $ sudo cp /etc/network/interfaces /etc/network/interfaces~
2. Bootstrap a local environment with default config
3. After machine-0 is running in $ juju status, ensure the /etc/network/interfaces and /etc/network/interfaces~ differ
4. Destroy the environment and replace your interfaces file with the backup (no need to start or stop anything I think), possibly also removing /etc/network/interfaces.d/*.cfg the networker created.