PaperMC/paper-server/nms-patches/net/minecraft/server/commands/CommandSummon.patch

--- a/net/minecraft/server/commands/CommandSummon.java
+++ b/net/minecraft/server/commands/CommandSummon.java
@@ -65,7 +65,7 @@
                     ((EntityInsentient) entity).finalizeSpawn(commandlistenerwrapper.getLevel(), commandlistenerwrapper.getLevel().getCurrentDifficultyAt(entity.blockPosition()), EnumMobSpawn.COMMAND, (GroupDataEntity) null, (NBTTagCompound) null);
                 }
 
-                if (!worldserver.tryAddFreshEntityWithPassengers(entity)) {
+                if (!worldserver.tryAddFreshEntityWithPassengers(entity, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.COMMAND)) { // CraftBukkit - pass a spawn reason of "COMMAND"
                     throw CommandSummon.ERROR_DUPLICATE_UUID.create();
                 } else {
                     commandlistenerwrapper.sendSuccess(new ChatMessage("commands.summon.success", new Object[]{entity.getDisplayName()}), true);