diff --git a/.gitignore b/.gitignore
index 83e8a08..bece568 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,3 +23,5 @@ parsetab_*
 .tox
 .eggs/
 venv/
+.\#*
+\#*\#
\ No newline at end of file
diff --git a/ming/odm/mapper.py b/ming/odm/mapper.py
index 735328b..b79eff0 100644
--- a/ming/odm/mapper.py
+++ b/ming/odm/mapper.py
@@ -87,6 +87,9 @@ def update(self, obj, state, session, **kwargs):
         doc = self.collection(state.document, skip_from_bson=True)
         ret = session.impl.save(doc, validate=False, state=state)
         state.status = state.clean
+        # Make sure that st.document is never the same as st.original_document
+        # otherwise mutating one mutates the other.
+        state.original_document = deepcopy(doc)
         return ret
 
     @_with_hooks('delete')
@@ -183,8 +186,6 @@ def _from_doc(self, doc, options, validate=True):
 
         # Make sure that st.document is never the same as st.original_document
         # otherwise mutating one mutates the other.
-        # There is no need to deepcopy as nested mutable objects are already
-        # copied by InstrumentedList and InstrumentedObj to instrument them.
         st.original_document = deepcopy(doc)
 
         if validate is False:
diff --git a/ming/session.py b/ming/session.py
index 9af9ecf..7a829b7 100644
--- a/ming/session.py
+++ b/ming/session.py
@@ -14,6 +14,7 @@
 
 log = logging.getLogger(__name__)
 
+
 def annotate_doc_failure(func):
     '''Decorator to wrap a session operation so that any pymongo errors raised
     will note the document that caused the failure
@@ -30,7 +31,7 @@ def wrapper(self, doc, *args, **kwargs):
     return update_wrapper(wrapper, func)
 
 
-class Session(object):
+class Session:
     _registry = {}
     _datastores = {}
 
@@ -152,15 +153,13 @@ def _prep_save(self, doc, validate):
         return data
 
     @annotate_doc_failure
-    def save(self, doc, state=None, **kwargs):
-        # args was meant to be the list of changed fields
-        # but actually we ended up checking the differences here
+    def save(self, doc, *args, state=None, **kwargs):
         data = self._prep_save(doc, kwargs.pop('validate', True))
-        if state is not None and state.original_document:
-            if state is not None:
-                args = tuple(set((k for k, v in
-                                  doc_to_set(state.original_document)
-                                  ^ doc_to_set(data))))
+        if not args and state is not None and state.original_document:
+            args = tuple(set((k for k, v in
+                              doc_to_set(state.original_document)
+                              ^ doc_to_set(data))))
+        if args:
             values = dict((arg, data[arg]) for arg in args)
             result = self._impl(doc).update(
                 dict(_id=doc._id), {'$set': values}, **fix_write_concern(kwargs))
diff --git a/ming/tests/odm/test_mapper.py b/ming/tests/odm/test_mapper.py
index e8055a7..0c202da 100644
--- a/ming/tests/odm/test_mapper.py
+++ b/ming/tests/odm/test_mapper.py
@@ -277,6 +277,23 @@ def test_group(self, pymongo_group):
         self.Basic.query.group()
         assert pymongo_group.called
 
+    def test_multiple_update_flushes(self):
+        initial_doc = self.Basic()
+        initial_doc.a = 1
+        self.session.flush()
+        self.session.close()
+
+        doc_updating = self.Basic.query.get(_id=initial_doc._id)
+        doc_updating.a = 2
+        self.session.flush()
+        doc_updating.a = 1  # back to "initial" value
+        doc_updating.e = 'foo'  # change something else too
+        self.session.flush()
+        self.session.close()
+
+        doc_after_updates = self.Basic.query.get(_id=doc_updating._id)
+        assert doc_after_updates.a == 1
+
 
 class TestRelation(TestCase):
     def setUp(self):
diff --git a/setup.cfg b/setup.cfg
index ebde9bc..1be30d6 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,3 +1,6 @@
+[pylint]
+# disabling protected-access because of mongodb _id property
+disable = protected-access
 
 [nosetests]
 detailed-errors=1