Index: src/wp-admin/includes/plugin.php
===================================================================
--- src/wp-admin/includes/plugin.php	(revision 42610)
+++ src/wp-admin/includes/plugin.php	(working copy)
@@ -1133,7 +1133,7 @@
 
 	$menu_slug = plugin_basename( $menu_slug );
 
-	$admin_page_hooks[ $menu_slug ] = sanitize_title( $menu_title );
+	$admin_page_hooks[ $menu_slug ] = $menu_slug;
 
 	$hookname = get_plugin_page_hookname( $menu_slug, '' );
 
Index: tests/phpunit/tests/admin/includesPlugin.php
===================================================================
--- tests/phpunit/tests/admin/includesPlugin.php	(revision 42610)
+++ tests/phpunit/tests/admin/includesPlugin.php	(working copy)
@@ -57,6 +57,19 @@
 		wp_set_current_user( $current_user );
 	}
 
+	function test_sub_menu_page_hookname_should_include_parent_menu_slug() {
+
+		$parent_menu_slug = 'mt-top-level';
+		$child_menu_slug = 'sub-page';
+
+		add_menu_page( 'Test Toplevel', 'Test Toplevel', 'manage_options', $parent_menu_slug, 'mt_toplevel_page' );
+		add_submenu_page( 'mt-top-level-handle', 'Test Sublevel', 'Test Sublevel', 'manage_options', $child_menu_slug, 'mt_sublevel_page' );
+
+		$child_menu_hookname = get_plugin_page_hookname( $child_menu_slug, $parent_menu_slug );
+		$this->assertEquals( $child_menu_hookname, "${parent_menu_slug}_page_${child_menu_slug}" );
+
+	}
+
 	function test_is_plugin_active_true() {
 		activate_plugin( 'hello.php' );
 		$test = is_plugin_active( 'hello.php' );