'There is no task provider registered for tasks of type "cargo".' in VS Code code-workspaces

[oeed]

In version 0.2.620 & 0.2.621 Cargo tasks configured using a VS Code .code-workspace file appear to not be working; rolling back to 0.2.612 does not have this issue. The workspace does have multiple root folders.

When attempting to run one I get an error notification stating: There is no task provider registered for tasks of type "cargo".
the following is shown also shown in the 'Tasks' output:

Error: The cargo task detection didn't contribute a task for the following configuration:
{
    "type": "cargo",
    "command": "build",
    "problemMatcher": [
        "$rustc"
    ],
    "group": "build",
    "label": "in .code-workspace"
}
The task will be ignored.

.code-workspace configured as such:

{
  "tasks": {
    "version": "2.0.0",
    "tasks": [
      {
        "type": "cargo",
        "command": "build",
        "problemMatcher": [
          "$rustc"
        ],
        "group": "build",
        "label": "in .code-workspace"
      }
    ]
  }
}

Strangely tasks work fine from a tasks.json file though.

{
  "version": "2.0.0",
  "tasks": [
    {
      "type": "cargo",
      "command": "build",
      "problemMatcher": [
        "$rustc"
      ],
      "group": "build",
      "label": "in tasks.json"
    }
  ]
}