gistfile1

diff -r 8201108e9cf0 src/eval.c
--- a/src/eval.c	Tue May 01 21:14:34 2012 +0200
+++ b/src/eval.c	Thu May 03 03:00:30 2012 +0900
@@ -10110,7 +10110,7 @@
 	l1 = argvars[0].vval.v_list;
 	l2 = argvars[1].vval.v_list;
 	if (l1 != NULL && !tv_check_lock(l1->lv_lock, (char_u *)_(arg_errmsg))
-		&& l2 != NULL)
+		&& l2 != NULL && l1 != l2)
 	{
 	    if (argvars[2].v_type != VAR_UNKNOWN)
 	    {
@@ -10149,7 +10149,7 @@
 	d1 = argvars[0].vval.v_dict;
 	d2 = argvars[1].vval.v_dict;
 	if (d1 != NULL && !tv_check_lock(d1->dv_lock, (char_u *)_(arg_errmsg))
-		&& d2 != NULL)
+		&& d2 != NULL && d1 != d2)
 	{
 	    /* Check the third argument. */
 	    if (argvars[2].v_type != VAR_UNKNOWN)
@@ -10191,7 +10191,7 @@
 			EMSG2(_("E737: Key already exists: %s"), hi2->hi_key);
 			break;
 		    }
-		    else if (*action == 'f')
+		    else if (*action == 'f' && HI2DI(hi2) != di1)
 		    {
 			clear_tv(&di1->di_tv);
 			copy_tv(&HI2DI(hi2)->di_tv, &di1->di_tv);