Linux: "Missing key 'natives-linux' on libraries[*].downloads" when downloading versions 1.8 and lower

Trying to download the client for 1.8.x with the 2.0.1005-dev-linux client fails with the error message.

Error details: Missing key 'natives-linux' on libraries[*].downloads (should be object, required as there's a classifier)

No 1.8 folder is created under versions, and no jar files are downloaded.

Newer versions 1.9 - 1.12.2 all seem to work fine, but can not download and launch a 1.8.x client for regression testing.