Setting diagram.UndoRedoService.UndoBufferSize to 0 after doing some undoable action in diagram does not stop the undo operations. This is a regression issue. Expected: UndoBufferSize 0 means no undo possible. RedoBufferSize 0 means no redo possible. Worakround if applicable: Set the UndoBufferSize to 0 after InitializeComponent. (this is if you don't need undo/redo at all).