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Relation of the issue types is as following:

If you've added sub-tasks to an issue, and need to reorder them, you can drag and drop them on the issue navigator view of the parent issue.
If you're using a board in Jira Software, you can also reorder the sub-tasks on the board view. However, these two methods are independent of each other. Reordering sub-tasks on the parent issue will not reorder tasks on an existing board, and vice-versa.

Additionally, Jira Service management adds four more standard types for support projects.

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