When viewing a list, such as shown above, the filtered fields set are dependent upon the work item type being displayed in the list. In the above example, only fields on the User Story work item (HierarchicalRequirement in the Web Services API doc) are available to filter.
The Task Status field is a calculated field on the User Story work item that will always be:
- “Defined” only if all Tasks are Defined
- “Completed” only if all Tasks are Completed
- “In-Progress” if one or more Task is In-Progress