This is not a slip up. There is a lot of effort that would need to go in refactoring the code in such a way that it would use the RadixJoinTransformation. Since we overhead the effort of an overhaul of the query parsing, we decided to put this of to a later point in time.
This has now been renamed into a FIXME.
If this is not according to the project's guideline, let me know and we work out a solution.