Add an accessor to make the intent more clear here

Library/Homebrew/options.rb

@@ -50,13 +50,16 @@ end
 class Options
   include Enumerable
 
+  attr_reader :options
+  protected :options
+
   def initialize(*args)
     @options = Set.new(*args)
   end
 
   def initialize_copy(other)
     super
-    @options = @options.dup
+    @options = other.options.dup
   end
 
   def each(*args, &block)