jb = The authors initials.
It should work, I don't see anything out of the ordinary. It changes the blocks objects to layer 0, and then it searchs the block collection (which is where the definition for the spaces are) and if it finds your block, it changes it to the new layer. The only thing I can think of is that your block is a nested one, or with the new dynamic blocks. If the block is a dynamic one, and has been changed, then the name isn't the one that defines it.
Hope that makes sense.