Hi,
Regarding the UML-RT specific diagrams on the "New Diagram..." menu is apparently pretty confusing. I wrote
bug 511187 to track some improvements in this area, specifically regarding the creation of state-machine diagrams. The existence of the possibility of creating UML-RT specific diagrams on the "New Diagram..." menu have never been intentional (if it ever have been possible). We for example removed the possibility of creating these diagram types in the new model wizard, since it does not make sense to create a "stand alone" capsule structure diagram, or state-machine diagram, without a capsule or state-machine. See for example the discussion in
bug 475805. The creation of these diagrams have always been intended to be made automatically when creating the capsule or the state-machine. But apparently this seem to be confusing.
So if users expect the possibility of being able to create the diagrams directly, then we probably should extend
bug 511187 to also cover the creation of capsule structure diagrams. But the behavior then should of course be to create the capsule (at the location where the user selects to create the diagram) and then as usual let the creation of the capsule create its owned/nested capsule structure diagrams. We should probably also think through whether we shall have a specific, "New UML-RT Diagram..." menu, similar to the specific "New UML-RT Child..." menu, to make it clear where you find the standard UML stuff, vs. the UML-RT specific stuff.
Some more comments inline below.