Cloning/Duplicating an Issue with subtasks should allow to clone/duplicate the sub-tasks as well
When a parent issue is cloned/duplicated, the subtasks/children are not processed.
This should be modified, to allow either clone a parent alone, or with all children, leading to a deep clone of the entire issue tree.
Right now, an issue can only be cloned by itself. If, for whatever reason, you want to create a copy of an entire issue tree, you'll have to copy every issue by hand and re-create the parent-child relations in each of cloned issues.