Frank, I have had this issue if the scenario I’m posting is not the default scenario. When posting non-default scenarios, member properties often don’t get updated. (Maybe never.)
Are you posting the default scenario?
If not, you can make this scenario the default, then post the data, then put the default scenario back to the real default to keep from messing up any other dependencies. Just keep in mind that with member properties you’re changing all objects in your scenario, even if that object shared with another scenario, since the attributes may be scenario specific, but member properties are not.