The list of autoUpdated cursor is static and shared between mutiple editor.
So if i have two editor open, and copy 3 selected line from one editor to another, and i look the first editor, the selection is modified. If i undo the paste in the second editor (with Ctrl+Z), the selection is restored in the first editor
See static QList<QDocumentCursorHandle*> m_autoUpdated;
Do you want more detail ?