fix subprojects are not copied correctly

[``* `#15173` Subprojects are not copied correctly``](http://www.openproject.org/work_packages/15173)
@0xF013 I guess it makes sense to write an expectation that the user issuing the copying gets set in order to make the tests more reliant. In addition to that, and that is only to prevent this spec from influencing the spec running after it, I would also preserve the stubbing.