Leave hash arguments unmodified.

lib/mongo/db.rb

@@ -296,6 +296,7 @@ module Mongo
       if strict? && !collection_names.include?(name)
         raise Mongo::MongoDBError, "Collection #{name} doesn't exist. Currently in strict mode."
       else
+        opts = opts.dup
         opts[:safe] = opts.fetch(:safe, @safe)
         opts.merge!(:pk => @pk_factory) unless opts[:pk]
         Collection.new(name, self, opts)

lib/mongo/gridfs/grid.rb

@@ -65,6 +65,7 @@ module Mongo
     #
     # @return [Mongo::ObjectId] the file's id.
     def put(data, opts={})
+      opts     = opts.dup
       filename = opts[:filename]
       opts.merge!(default_grid_io_opts)
       file = GridIO.new(@files, @chunks, filename, 'w', opts=opts)

test/grid_file_system_test.rb

@@ -12,6 +12,22 @@ class GridFileSystemTest < Test::Unit::TestCase
       @db.drop_collection('fs.chunks')
     end
 
+    context "Initialization" do
+      setup do
+        @chunks_data = "CHUNKS" * 50000
+        @grid = GridFileSystem.new(@db)
+        @opts = {:safe => true}
+        @original_opts = @opts.dup
+        @grid.open('sample.file', 'w', @opts) do |f|
+          f.write @chunks_data
+        end
+      end
+
+      should "not modify original opts" do
+        assert_equal @original_opts, @opts
+      end
+    end
+
     context "When reading:" do
       setup do
         @chunks_data = "CHUNKS" * 50000