In general, undo operations are organized per ArcGIS.Desktop.Framework.Contracts.Pane and ArcGIS.Desktop.Framework.Contracts.DockPane. In other words, each Pane and DockPane manages its own operation stack. For example, operations added to map A are not visible to map B. The active window (Pane or DockPane) becomes the active OperationManager. When a window becomes active, its OperationManager is requested and connected to the undo/redo user interface.
Panes and DockPanes may however elect to share OperationManagers. For example, two Panes that are showing the same map will have the same OperationManager.
System.Object
ArcGIS.Desktop.Framework.OperationManager
ArcGIS.Desktop.Framework.CompositeOperationManager
Target Platforms: Windows 10, Windows 8.1, Windows 7