3171536 - How are my manually added approvers retained on new requisition versions and after post-submission edits?

I want to understand how manually added approvers behave when a requisition's approval flow is regenerated.

I notice that an approver I manually added to a requisition still appears when a new version is created (for example, on version 2 of the requisition), or after a post-submission edit causes the approval flow to be resubmitted. 
In some cases, the manually added approver appears in parallel with the remaining approvers rather than in the serial position where I originally placed the approver. I want to know why this happens, whether it is expected, and what determines whether a manually added approver is preserved across new versions or removed.

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