ok, this is a zend bug.

ext/simplexml/examples/book.php

@@ -1,6 +1,7 @@
 <?php
-$books = simplexml_load_file('book.xml')->book;
-
+$books = simplexml_load_file('book.xml');
+//var_dump($books);
+$books = $books->book;
 foreach ($books as $book) {
 	echo "{$book->title} was written by {$book->author}\n";
 }

ext/simplexml/simplexml.c

@@ -783,13 +783,14 @@ sxe_object_dtor(void *object, zend_object_handle handle TSRMLS_DC)
 
 	sxe = (php_sxe_object *) object;
 
+	FREE_HASHTABLE(sxe->zo.properties);
+
 	if (--sxe->document->refcount > 0) {
 		return;
 	}
-	
 	xmlFreeDoc(sxe->document->ptr);
-	FREE_HASHTABLE(sxe->zo.properties);
-
+	efree(sxe->document);
+		
 	if (sxe->xpath) {
 		xmlXPathFreeContext(sxe->xpath);
 	}
@@ -858,8 +859,8 @@ PHP_FUNCTION(simplexml_load_file)
 
 	sxe = php_sxe_object_new(TSRMLS_C);
 	sxe->document = emalloc(sizeof(simplexml_ref_obj));
-	sxe->document->refcount = 1;
 	sxe->document->ptr = (void *) xmlParseFile(filename);
+	sxe->document->refcount = 1;
 	if (sxe->document->ptr == NULL) {
 		efree(sxe->document);
 		RETURN_FALSE;
@@ -893,7 +894,7 @@ PHP_FUNCTION(simplexml_load_string)
 		RETURN_FALSE;
 	}
 	sxe->nsmap = xmlHashCreate(10);
-		
+
 	return_value->type = IS_OBJECT;
 	return_value->value.obj = php_sxe_register_object(sxe TSRMLS_CC);
 }