When dragging and dropping a parent issue in the Portfolio 3.0 improved interface will only impact the rank for the issue you moved. The rank for all descendent issues will remain unchanged.
This behaviour used to be the default behaviour in 2.0 but was changed due to feedback (more info:
Allow the user to configure between the old ranking behaviour and the new ranking behaviour
- Drag an epic (with children) from the bottom of the plan to the top
- The child issues of the epic would be ranked to the top when viewing story <-> story.
- Auto-schedule would consider the child issues as high-priority.
- All child issues would also be ranked to the top - looking at only the story level issues, the child issues will remain ranked at the bottom
- Auto-schedule considers these issues last.
- Select the issue and all it's children
- Select Bulk actions
- Bulk change 'Rank'
- Set the new rank for all selected issues in the hierarchy