diff -r ed134fdfe95f -r 275a4428c13b librazor/merger.c
--- a/librazor/merger.c	Wed Apr 28 11:59:02 2010 +0100
+++ b/librazor/merger.c	Tue Mar 27 21:32:46 2012 +0100
@@ -1,7 +1,7 @@
 /*
  * Copyright (C) 2008  Kristian Høgsberg <krh@redhat.com>
  * Copyright (C) 2008  Red Hat, Inc
- * Copyright (C) 2009, 2010  J. Ali Harlow <ali@juiblex.co.uk>
+ * Copyright (C) 2009-2011  J. Ali Harlow <ali@juiblex.co.uk>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -47,9 +47,18 @@
 	struct razor_merger *merger;
 	int count;
 	size_t size;
+	uint32_t header_version;
 
 	merger = zalloc(sizeof *merger);
 	merger->set = razor_set_create();
+	if (set1->packages.size) {
+		header_version = razor_set_get_header_version(set1);
+		if (set2->packages.size &&
+		    razor_set_get_header_version(set2) > header_version)
+			header_version = razor_set_get_header_version(set2);
+	} else
+		header_version = razor_set_get_header_version(set2);
+	razor_set_set_header_version(merger->set, header_version);
 	hashtable_init(&merger->table, &merger->set->string_pool);
 	hashtable_init(&merger->file_table, &merger->set->file_string_pool);
 	hashtable_init(&merger->details_table,
@@ -592,16 +601,24 @@
 
 	switch (script) {
 	case RAZOR_PROPERTY_PREUN:
-		assert(pool[package->preun.program] == '\0');
-		assert(pool[package->preun.body] == '\0');
-		package->preun.program = p;
-		package->preun.body = b;
+		if (package->preun.program != p) {
+			assert(pool[package->preun.program] == '\0');
+			package->preun.program = p;
+		}
+		if (package->preun.body != b) {
+			assert(pool[package->preun.body] == '\0');
+			package->preun.body = b;
+		}
 		break;
 	case RAZOR_PROPERTY_POSTUN:
-		assert(pool[package->postun.program] == '\0');
-		assert(pool[package->postun.body] == '\0');
-		package->postun.program = p;
-		package->postun.body = b;
+		if (package->postun.program != p) {
+			assert(pool[package->postun.program] == '\0');
+			package->postun.program = p;
+		}
+		if (package->postun.body != b) {
+			assert(pool[package->postun.body] == '\0');
+			package->postun.body = b;
+		}
 		break;
 	default:
 		break;