Some of the specs (cached libraries and user permissions to add libs) fail on MRI as well, but i see an encoding issue you may want to take a look at.
I wonder if an RBX-optimized version leveraging LLVM and the JIT could be used to create on libraries on the fly, optimized for our conditions. Somewhat like metasm, but a lot faster.
Closing this one as the specs fail on MRI as well and it's not entirely clear whether this is an Rbx issue or not. Feel free to re-open this issue if needed.