Unable to rank sub-task higher than parent task in another column

Summary

If there's a story in specific column of a Kanban board with sub-tasks, when the subtask is moved to another column user will not be able to rank it higher or lower by dragging it. But user can still change the rank by moving the stories above and below the sub-task.

Environment

JIRA 7.1.6, JIRA 6.4.13

Expected Results

User should be able to drag the sub-task to change the rank in a column

Actual Results

User is not able to change the rank because the subtask can't be moved.

Workaround

Move the stories above or below the sub-task to re-rank the sub-task.