diff --git a/frappe/__init__.py b/frappe/__init__.py
index a0b5105554..aa45b0c86d 100644
--- a/frappe/__init__.py
+++ b/frappe/__init__.py
@@ -13,7 +13,7 @@ import os, sys, importlib, inspect, json
 from .exceptions import *
 from .utils.jinja import get_jenv, get_template, render_template
 
-__version__ = '7.1.20'
+__version__ = '7.1.21'
 __title__ = "Frappe Framework"
 
 local = Local()
diff --git a/frappe/model/base_document.py b/frappe/model/base_document.py
index f80f267961..ce05538360 100644
--- a/frappe/model/base_document.py
+++ b/frappe/model/base_document.py
@@ -517,7 +517,16 @@ class BaseDocument(object):
 			values = frappe.db.get_value(self.doctype, self.name, constants, as_dict=True)
 
 		for fieldname in constants:
-			if self.get(fieldname) != values.get(fieldname):
+			df = self.meta.get_field(fieldname)
+
+			# This conversion to string only when fieldtype is Date 
+			if df.fieldtype == 'Date':
+				value = str(values.get(fieldname))
+
+			else:
+				value  = values.get(fieldname)
+
+			if self.get(fieldname) != value:
 				frappe.throw(_("Value cannot be changed for {0}").format(self.meta.get_label(fieldname)),
 					frappe.CannotChangeConstantError)
 
diff --git a/frappe/model/document.py b/frappe/model/document.py
index 2c57892adc..340cee8ac8 100644
--- a/frappe/model/document.py
+++ b/frappe/model/document.py
@@ -285,12 +285,16 @@ class Document(BaseDocument):
 			return
 
 		if rows:
-			# delete rows that do not match the ones in the
-			# document
-			frappe.db.sql("""delete from `tab{0}` where parent=%s
+			# select rows that do not match the ones in the document
+			deleted_rows = frappe.db.sql("""select name from `tab{0}` where parent=%s
 				and parenttype=%s and parentfield=%s
 				and name not in ({1})""".format(df.options, ','.join(['%s'] * len(rows))),
 					[self.name, self.doctype, fieldname] + rows)
+			if len(deleted_rows) > 0:
+				# delete rows that do not match the ones in the document
+				frappe.db.sql("""delete from `tab{0}` where name in ({1})""".format(df.options,
+					','.join(['%s'] * len(deleted_rows))), tuple(row[0] for row in deleted_rows))
+
 		else:
 			# no rows found, delete all rows
 			frappe.db.sql("""delete from `tab{0}` where parent=%s