Index: sys/kern/kern_shutdown.c
===================================================================
--- sys/kern/kern_shutdown.c
+++ sys/kern/kern_shutdown.c
@@ -427,6 +427,7 @@
 kern_reboot(int howto)
 {
 	static int once = 0;
+	static int handler_once = 0;
 
 	/*
 	 * Normal paths here don't hold Giant, but we can wind up here
@@ -480,7 +481,10 @@
 	 * Ok, now do things that assume all filesystem activity has
 	 * been completed.
 	 */
-	EVENTHANDLER_INVOKE(shutdown_post_sync, howto);
+	if (handler_once == 0) {
+		handler_once = 1;
+		EVENTHANDLER_INVOKE(shutdown_post_sync, howto);
+	}
 
 	if ((howto & (RB_HALT|RB_DUMP)) == RB_DUMP && !cold && !dumping) 
 		doadump(TRUE);