Steps to reproduce
Right-click on a document and click Version History.
The document’s previous versions (displayed on left) have their items and sub-items listed in the same order as the document’s current version (displayed on the right)
For most (not all) of my documents, the previous versions have their items (and subitems, recursively) listed in reverse order. Therefore in order to fully restore a previous version of a document with many levels of hierarchy, I would need to not only copy and paste the OPML but then right-click on every item which contains multiple children, and click Sort > Reverse Current. This makes Version History almost useless for reverting complex documents.
Windows 10, Google Chrome, no third-party scripts