When you try to copy a Ruby hash using .dup or .clone, you get what is called a "shallow" copy. The data in the hash below the first level just seems to be referenced, so if you have a hash within the hash, and try to change a value in the deeper hash, the value is changed even for the original hash you ran the .dup on. To get a full ("deep") copy of a hash, you have to run an inelegant hack using Marshal to copy it: copy_hash = (Marshal.load(Marshal.dump(source_hash))). This apparently applies to arrays too. See the code below for an example, and I hope this saves you hours of debugging.
