PlanManager: drop spurious items for unexpected mission types (#10509)

* PlanManager: drop spurious items for unexpected mission types
* PlanManager: drive-by bug fix

src/MissionManager/PlanManager.cc

@@ -375,6 +375,7 @@ void PlanManager::_handleMissionItem(const mavlink_message_t& message)
 {
     MAV_CMD          command;
     MAV_FRAME        frame;
+    MAV_MISSION_TYPE missionType;
     double           param1;
     double           param2;
     double           param3;
@@ -389,8 +390,9 @@ void PlanManager::_handleMissionItem(const mavlink_message_t& message)
     mavlink_mission_item_int_t missionItem;
     mavlink_msg_mission_item_int_decode(&message, &missionItem);
 
-    command =       (MAV_CMD)missionItem.command,
-            frame =         (MAV_FRAME)missionItem.frame,
+    command =       (MAV_CMD)missionItem.command;
+    frame =         (MAV_FRAME)missionItem.frame;
+    missionType =   (MAV_MISSION_TYPE)missionItem.mission_type;
     param1 =        missionItem.param1;
     param2 =        missionItem.param2;
     param3 =        missionItem.param3;
@@ -402,6 +404,13 @@ void PlanManager::_handleMissionItem(const mavlink_message_t& message)
     isCurrentItem = missionItem.current;
     seq =           missionItem.seq;
 
+    // Check the mission_type field. It can happen that we receive a late duplicate message for a
+    // different mission_type request.
+    if (missionType != _planType) {
+       qCDebug(PlanManagerLog) << QStringLiteral("_handleMissionItem %1 dropping spurious item seq:command:missionType").arg(_planTypeString()) << seq << command << missionType;
+       return;
+    }
+
     // We don't support editing ALT_INT frames so change on the way in.
     if (frame == MAV_FRAME_GLOBAL_INT) {
         frame = MAV_FRAME_GLOBAL;