Issue Summary

When a subtask is part of the source issues of an advanced roadmap but its parent task is not, the subtask is not displayed but it is still there.

This is reproducible on Data Center: (yes) / (no)

Steps to Reproduce

1. Create a filter to include a subtask but not its parent
2. Created a roadmap using that filter
3. the subtask is not visible until you select "Subtasks to subtasks" in the filter hierarchy option.
   
4. however, the subtask is still considered for any action in the roadmap.
   

Expected Results

The subtask should appear in a section: "orphan subtasks" similar to the stories without Epics, or Epics without Initiatives:

Actual Results

The subtasks are not shown at all.

Workaround

Modify the source filter to include the parent of subtasks.