Fixed slice when using inheritance causing fields to be excluded (#437)

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 
 Changes in 0.8.4
 ================
+- Fixed slice when using inheritance causing fields to be excluded (#437)
 - Fixed ._get_db() attribute after a Document.switch_db() (#441)
 - Dynamic Fields store and recompose Embedded Documents / Documents correctly (#449)
 - Handle dynamic fieldnames that look like digits (#434)

mongoengine/queryset/field_list.py

@@ -55,6 +55,7 @@ class QueryFieldList(object):
 
         if self.always_include:
             if self.value is self.ONLY and self.fields:
+                if sorted(self.slice.keys()) != sorted(self.fields):
                     self.fields = self.fields.union(self.always_include)
             else:
                 self.fields -= self.always_include