Not a high priority bug but probably still needs to be fixed.

When creating a link between two table nodes, if you set the OriginIndex before you assign a destination node to the link a NullReferenceException is thrown.

The code below throws the exception:
DiagramLink lnk1 = new DiagramLink(diagram1);
lnk1.Origin = nde1;
lnk1.OriginIndex = 0;  // exception thrown here
lnk1.Destination = nde2;
lnk1.DestinationIndex = 1;
diagram1.Links.Add(lnk1);

You need to assign the destination node first:
DiagramLink lnk1 = new DiagramLink(diagram1);
lnk1.Origin = nde1;
lnk1.Destination = nde2;
lnk1.OriginIndex = 0;
lnk1.DestinationIndex = 1;
diagram1.Links.Add(lnk1);