Restarting image import leaves boot-resources empty (selection is made but not saved)

Sometimes in the CI, boot resources do not start downloading. In the UI, the selections are still shown, but the button says 'Save Selections' indicating that they have not been persisted. In the CLI, boot-sources and boot-source-selections both return something sensible, but boot-resources is empty:

root@autopkgtest:/home/ubuntu# maas maas boot-sources read
Success.
Machine-readable output follows:
[
    {
        "id": 1,
        "updated": "2016-11-10T07:18:22.487",
        "keyring_filename": "/usr/share/keyrings/ubuntu-cloudimage-keyring.gpg",
        "keyring_data": "",
        "created": "2016-11-10T07:18:22.487",
        "url": "http://images.maas.io/ephemeral-v3/daily/",
        "resource_uri": "/MAAS/api/2.0/boot-sources/1/"
    }
]
root@autopkgtest:/home/ubuntu# maas maas boot-source-selections read 1
Success.
Machine-readable output follows:
[
    {
        "resource_uri": "/MAAS/api/2.0/boot-sources/1/selections/1/",
        "arches": [
            "amd64"
        ],
        "os": "ubuntu",
        "subarches": [
            "*"
        ],
        "labels": [
            "*"
        ],
        "release": "xenial",
        "id": 1
    }
]
root@autopkgtest:/home/ubuntu# maas maas boot-resources read
Success.
Machine-readable output follows:
[]

Restarting the import again with stop-import and import calls, seems to make things work again.