I'm seeing the following message frequently in my logs, "PCP: External IP in request didn't match interface IP". I'm also seeing Back to My Mac fail to create any mappings.
This seems to match an issue in miniupnpd (https://github.com/miniupnp/miniupnp/issues/69), which was resolved in the 1.9 release (released on 2014/10/27). Since the miniupnpd in EdgeOS is older, (1.8.20140203-ubnt7) this issue still affects these devices.