In deriver.rb the code for -

def pivot_currency
  @pivot_currency || @source.pivot_currency || :USD
end

should be -

def pivot_currency
  @source.pivot_currency || @pivot_currency || :USD
end

The variable @pivot_currency is initialized to :USD by base.rb in the super initialize. It is set to nil in the class
initialized, but this is overwritten by base.rb.

This means that the pivot currency will always be USD, even if the @source.pivot_currency is different.