Fix clear_changed_fields() clearing unsaved documents bug #602

AUTHORS

@@ -196,3 +196,4 @@ that much better:
  * Polyrabbit (https://github.com/polyrabbit)
  * Sagiv Malihi (https://github.com/sagivmalihi)
  * Dmitry Konishchev (https://github.com/KonishchevDmitry)
+ * Martyn Smith (https://github.com/martynsmith)

docs/changelog.rst

@@ -6,6 +6,7 @@ Changelog
 Changes in 0.9.X - DEV
 ======================
 
+- Fix clear_changed_fields() clearing unsaved documents bug #602
 - Removing support for Django 1.4.x, pymongo 2.5.x, pymongo 2.6.x.
 - Removing support for Python < 2.6.6
 - Fixed $maxDistance location for geoJSON $near queries with MongoDB 2.6+ #664

mongoengine/base/document.py

@@ -407,6 +407,8 @@ class BaseDocument(object):
                 else:
                     data = getattr(data, part, None)
                 if hasattr(data, "_changed_fields"):
+                    if hasattr(data, "_is_document") and data._is_document:
+                        continue
                     data._changed_fields = []
         self._changed_fields = []