Take a look a this diagram, and note these nodes on top: father (ia:123), mother (ia:124) and standalone (ia_1000042_ia125_has_father_123). They are positioned the way I want, but I also want to attach the standalone node as an Association Node on the has_father relation.
To do this, edit the source at the above link and put this line before @enduml:
(ia_1000042, ia_123) . ia_1000042_ia125_has_father_123
As a result, the father & mother nodes drop below the ia:1000042 node, and the has_father relation has wrong direction! This contradicts the following:
ia_1000042 -up-> ia_123 : gvp:ia125_has_father