The Data/ folder isn't part of the distribution in the OSX installer. That means GlyphConstructions?.txt is missing and certain functions in RoboFab can't work. The problem is that the Data folder isn't part of the actual code. In the previous install-with-a-script method, the robofab library wasn't installed in site-packages, but left together with its other data. Workaround: make a Data/ folder in site-packages. Disadvantage: this is way too complicated for regular users.
Perhaps with the updated fontTools we can think of a different packaging strategy.