--- a/src/newgrf_callbacks.h	Thu Jul 05 05:41:56 2007 +0000
+++ b/src/newgrf_callbacks.h	Thu Jul 05 06:35:09 2007 +0000
@@ -12,6 +12,9 @@
  * Names are formatted as CBID_<CLASS>_<CALLBACK>
  */
 enum CallbackID {
+	/* Set when calling a randomizing trigger (almost undocumented) */
+	CBID_RANDOM_TRIGGER             = 0x01,
+
 	/* Powered wagons, if the result is lower as 0x40 then the wagon is powered
 	 * @todo : interpret the rest of the result, aka "visual effects" */
 	CBID_TRAIN_WAGON_POWER          = 0x10,

--- a/src/newgrf_engine.cpp	Thu Jul 05 05:41:56 2007 +0000
+++ b/src/newgrf_engine.cpp	Thu Jul 05 06:35:09 2007 +0000
@@ -1014,7 +1014,7 @@
 	assert(v != NULL);
 
 	NewVehicleResolver(&object, v->engine_type, v);
-
+	object.callback = CBID_RANDOM_TRIGGER;
 	object.trigger = trigger;
 
 	group = Resolve(GetVehicleSpriteGroup(v->engine_type, v), &object);