Hello Rafal
The "Use Parent Namespace" property of a package only applies to objects that can be owned by packages. Most (if not all) types of model have objects that can only be owned by the model, not by packages, such as Domains in data models, and organisation units in process models.
In your case, the model-level organisation units can be used by any package; I expected them to show up as shortcuts in the browser when I enabled the viewing of shortcuts, but they didn't. They do show up as dependencies in all the package diagrams that contain them.
It looks like your using the full BPMN 2 language, which I'm not familiar with, where the Participants and Organisation Units are model-level objects in my sample model