@Ashley: That's a relief then. But what about this?
The highlighted command seems to fail, even though both Cloud and RainCloud belong to CloudFamily, I even changed it to be explicitly Cloud->SetOpacity and it still failed.
I would have expected CloudFamily SOL to be the last created instance of a sprite belonging to that family.
If this is intentional, that's really unfortunate, it seems like I'm going to have to setup lots of duplicate code in each branch.