To reproduce: 
Bind using a binding source:
DataSet ds = new DataSet();
ds.Tables.Add(shapesTable);
ds.Tables.Add(connectionsTable);

BindingSource bindingSource1 = new BindingSource { DataSource = ds };

radDiagram1.DiagramElement.DataLayer.DataSource = bindingSource1;


Workaround: 
Bind directly:
DataSet ds = new DataSet();
ds.Tables.Add(shapesTable);
ds.Tables.Add(connectionsTable);

radDiagram1.DiagramElement.DataLayer.DataSource = ds;