--- a/nashorn/src/jdk/nashorn/internal/runtime/PropertyMap.java	Fri May 03 22:48:53 2013 +0200
+++ b/nashorn/src/jdk/nashorn/internal/runtime/PropertyMap.java	Fri May 03 22:50:51 2013 +0200
@@ -744,12 +744,7 @@
      * @return New {@link PropertyMap} with prototype changed.
      */
     PropertyMap changeProto(final ScriptObject oldProto, final ScriptObject newProto) {
-        if ((oldProto == newProto) ||
-            (size() == 0 &&
-             oldProto == null &&
-             protoGetSwitches == null &&
-             history == null &&
-             protoHistory == null)) {
+        if (oldProto == newProto) {
             return this;
         }
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nashorn/test/script/basic/JDK-8013874.js	Fri May 03 22:50:51 2013 +0200
@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ * 
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ * 
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ * 
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ * 
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * JDK-8013874: Function argument's prototype seem cached and wrongly reused
+ *
+ * @test
+ * @run
+ */
+
+function deepEqual(actual, expected) {
+    print("deepEqual: " + (actual.prop === expected.prop) + ", prop: " + expected.prop);
+}
+
+var proto = {};
+var other = {
+    prop: 0
+};
+
+function NameBuilder(first, last) {
+    this.first = first;
+    this.last = last;
+    return this;
+}
+
+NameBuilder.prototype = proto;
+
+function NameBuilder2(first, last) {
+    this.first = first;
+    this.last = last;
+    return this;
+}
+
+NameBuilder2.prototype = proto;
+
+var nb1 = new NameBuilder('Ryan', 'Dahl');
+var nb2 = new NameBuilder2('Ryan', 'Dahl');
+
+print("In loader, nb1.prop === nb2.prop " + (nb1.prop === nb2.prop));
+deepEqual(nb1, nb2);
+
+NameBuilder2.prototype = other;
+nb2 = new NameBuilder2('Ryan', 'Dahl');
+
+print("In loader, nb1.prop === nb2.prop " + (nb1.prop === nb2.prop));
+deepEqual(nb1, nb2);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nashorn/test/script/basic/JDK-8013874.js.EXPECTED	Fri May 03 22:50:51 2013 +0200
@@ -0,0 +1,4 @@
+In loader, nb1.prop === nb2.prop true
+deepEqual: true, prop: undefined
+In loader, nb1.prop === nb2.prop false
+deepEqual: false, prop: 0