--- a/src/ai/api/ai_order.cpp	Mon Mar 26 12:41:42 2007 +0000
+++ b/src/ai/api/ai_order.cpp	Mon Mar 26 12:58:47 2007 +0000
@@ -50,7 +50,7 @@
 {
 	switch (::GetOrderTypeByTile(destination)) {
 		case OT_GOTO_DEPOT:    return (order_flags & ~(AIOF_NON_STOP | AIOF_SERVICE_IF_NEEDED)) == 0;
-		case OT_GOTO_STATION:  return (order_flags & ~(AIOF_NON_STOP | AIOF_TRANSFER | AIOF_UNLOAD | AIOF_FULL_LOAD)) == 0;
+		case OT_GOTO_STATION:  return (order_flags & ~(AIOF_NON_STOP | AIOF_TRANSFER | AIOF_UNLOAD | AIOF_FULL_LOAD)) == 0 && ((order_flags & AIOF_UNLOAD) == 0 || (order_flags & AIOF_FULL_LOAD) == 0);
 		case OT_GOTO_WAYPOINT: return (order_flags & ~(AIOF_NON_STOP)) == 0;
 		default:               return false;
 	}
@@ -123,7 +123,16 @@
 	if (!IsValidVehicleOrder(vehicle_id, order_id) ||
 		!this->AreOrderFlagsValid(GetOrderDestination(vehicle_id, order_id), order_flags)) return false;
 
-	return this->DoCommand(0, vehicle_id | (order_id << 16), order_flags, CMD_MODIFY_ORDER);
+	for (;;) {
+		/* Loop as long as there is a difference between the requested and
+		 * the current orders of the vehicle. */
+		AIOrderFlags current = this->GetOrderFlags(vehicle_id, order_id);
+		AIOrderFlags diff = current ^ order_flags;
+		if (diff == 0) return true;
+
+		bool res = this->DoCommand(0, vehicle_id | (order_id << 16), FIND_FIRST_BIT(diff), CMD_MODIFY_ORDER);
+		if (!res) return false;
+	}
 }
 
 bool AIOrder::CopyOrders(VehicleID vehicle_id, VehicleID main_vehicle_id)

--- a/src/ai/api/ai_order.hpp	Mon Mar 26 12:41:42 2007 +0000
+++ b/src/ai/api/ai_order.hpp	Mon Mar 26 12:58:47 2007 +0000
@@ -26,9 +26,9 @@
 
 		/** Transfer instead of deliver the goods; only for stations. */
 		AIOF_TRANSFER          = 1 << 0,
-		/** Always unload the vehicle; only for stations. */
+		/** Always unload the vehicle; only for stations. Cannot be set when AIOF_FULL_LOAD is set. */
 		AIOF_UNLOAD            = 1 << 1,
-		/** Wait till the the vehicle is fully loaded; only for stations. */
+		/** Wait till the the vehicle is fully loaded; only for stations. Cannot be set when AIOF_UNLOAD is set. */
 		AIOF_FULL_LOAD         = 1 << 2,
 
 		/** Service the vehicle when needed, otherwise skip this order; only for depots. */