Overriding included manifest not straight forward

[brad]

I overrided pipeline's built-in manifest in order to make some local changes, and added pipeline.manifest.PipelineManifest to MANIFESTO_EXCLUDED_MANIFESTS but I was getting entries in the manifest from both PipelineManifest and my own local manifest LocalManifest. It turns out this was happening because I was importing pipeline.manifest.PipelineManifest in my own manifest.py for overriding, like so:

from pipeline.manifest import PipelineManifest`

class LocalManifest(PipelineManifest):

I managed to get the manifest to only include entries from LocalManifest by setting MANIFESTO_EXCLUDED_MANIFESTS like so:

MANIFESTO_EXCLUDED_MANIFESTS = (
    'pipeline.manifest.PipelineManifest',
    'my.local.manifest.PipelineManifest'
)

This is pretty non-intuitive, it seems like a bug in the manifest detection/exclusion mechanism to me.