Although the direct use of “ObjectNode” is discouraged in MD SysML, activity decomposition works in accordance with the SysML1.0 examples. See next image.
Corresponds with SysML1.0 examples, a single object appears to be owned by the usage context.
In fact a UML2 ObjectNode is abstract. Although the apparent ownership of an object by the higher activity context is consistent, it can't be represented using "elided Pin notation" in the activity diagram by MagicDraw UML.