I had a problem for a few days, where I was not able to add options to custom objects and I managed to reproduce it on one of the samples:
If you replace "urn:cr" with "abc:xyz" in the bundle-context.xml of the service as well as in the ModelObjectUriResolver (replace SCHEME with "abc" and NAMESPACE with "xyz"), then a right click on a Chassis in the view won't show any menu items.
This looks like a bug on the vSphere SDK side.