SpawnPotentials list working incorrectly

The new SpawnPotentials list works about 90% correctly. Mob Spawners with a SpawnPotentials list will properly cycle through the mob types in the list (as can be seen by the mob being displayed in the cage), but are spawned with the wrong EntityId. The spawner's base EntityId tag is used to spawn the entities in the list, instead of the provided Type variable. When saving and closing Minecraft, the current EntityId (depending on which one it is on in the cycle) gets saved to the map data, and is used for spawning new mobs when the map is reloaded. Below is the NBT structure of the spawner I have tested this with:

TAG_Compound({
  "MinSpawnDelay": TAG_Short(20),
  "MaxSpawnDelay": TAG_Short(80),
  "SpawnCount": TAG_Short(4),
  "id": TAG_String(u'MobSpawner'),
  "RequiredPlayerRange": TAG_Short(16),
  "Delay": TAG_Short(21),
  "MaxNearbyEntities": TAG_Short(6),
  "SpawnRange": TAG_Short(4),
  "SpawnPotentials": TAG_List([
    TAG_Compound({
      "Weight": TAG_Int(50),
      "Type": TAG_String(u'Skeleton'),
      "Properties": TAG_Compound({
        "HurtTime": TAG_Short(0),
        "IsVillager": TAG_Byte(0),
        "Air": TAG_Short(300),
        "CanPickUpLoot": TAG_Byte(0),
        "AttackTime": TAG_Short(0),
        "IsBaby": TAG_Byte(0),
        "PersistenceRequired": TAG_Byte(0),
        "Fire": TAG_Short(-1),
        "FallDistance": TAG_Float(0.0),
        "Invulnerable": TAG_Byte(0),
        "EntityId": TAG_String(u'Skeleton'),
      }),
    }),
    TAG_Compound({
      "Weight": TAG_Int(50),
      "Type": TAG_String(u'PigZombie'),
      "Properties": TAG_Compound({
        "DropChances": TAG_List([
          TAG_Float(1.0),
          TAG_Float(0.05000000074505806),
          TAG_Float(0.05000000074505806),
          TAG_Float(0.05000000074505806),
          TAG_Float(0.05000000074505806),
        ]),
        "Equipment": TAG_List([
          TAG_Compound({
            "id": TAG_Short(276),
            "Damage": TAG_Short(0),
            "Count": TAG_Byte(1),
            "tag": TAG_Compound({
              "ench": TAG_List([
                TAG_Compound({
                  "id": TAG_Short(16),
                  "lvl": TAG_Short(5),
                }),
              ]),
              "display": TAG_Compound({
                "Name": TAG_String(u'\xa7rRipper'),
                "Lore": TAG_List([
                  TAG_String(u'Of the Jack variety'),
                ]),
              }),
            }),
          }),
          TAG_Compound({
            "id": TAG_Short(301),
            "Damage": TAG_Short(0),
            "Count": TAG_Byte(1),
            "tag": TAG_Compound({
              "display": TAG_Compound({
                "color": TAG_Int(16776960),
              }),
            }),
          }),
          TAG_Compound({
            "id": TAG_Short(300),
            "Damage": TAG_Short(0),
            "Count": TAG_Byte(1),
            "tag": TAG_Compound({
              "display": TAG_Compound({
                "color": TAG_Int(255),
              }),
            }),
          }),
          TAG_Compound({}),
          TAG_Compound({}),
        ]),
        "HurtTime": TAG_Short(0),
        "IsVillager": TAG_Byte(0),
        "Air": TAG_Short(300),
        "CanPickUpLoot": TAG_Byte(0),
        "AttackTime": TAG_Short(0),
        "IsBaby": TAG_Byte(0),
        "PersistenceRequired": TAG_Byte(0),
        "Fire": TAG_Short(-1),
        "FallDistance": TAG_Float(0.0),
        "Invulnerable": TAG_Byte(0),
        "EntityId": TAG_String(u'PigZombie'),
      }),
    }),
    TAG_Compound({
      "Weight": TAG_Int(50),
      "Type": TAG_String(u'Zombie'),
      "Properties": TAG_Compound({
        "DropChances": TAG_List([
          TAG_Float(1.0),
          TAG_Float(0.05000000074505806),
          TAG_Float(0.05000000074505806),
          TAG_Float(0.05000000074505806),
          TAG_Float(0.05000000074505806),
        ]),
        "Equipment": TAG_List([
          TAG_Compound({
            "id": TAG_Short(279),
            "Damage": TAG_Short(0),
            "Count": TAG_Byte(1),
            "tag": TAG_Compound({
              "ench": TAG_List([
                TAG_Compound({
                  "id": TAG_Short(16),
                  "lvl": TAG_Short(5),
                }),
              ]),
              "display": TAG_Compound({
                "Name": TAG_String(u'\xa7rRipper'),
                "Lore": TAG_List([
                  TAG_String(u'Of the Jack variety'),
                ]),
              }),
            }),
          }),
          TAG_Compound({
            "id": TAG_Short(301),
            "Damage": TAG_Short(0),
            "Count": TAG_Byte(1),
            "tag": TAG_Compound({
              "display": TAG_Compound({
                "color": TAG_Int(16776960),
              }),
            }),
          }),
          TAG_Compound({}),
          TAG_Compound({}),
          TAG_Compound({
            "id": TAG_Short(298),
            "Damage": TAG_Short(0),
            "Count": TAG_Byte(1),
            "tag": TAG_Compound({
              "display": TAG_Compound({
                "color": TAG_Int(16711680),
              }),
            }),
          }),
        ]),
        "HurtTime": TAG_Short(0),
        "IsVillager": TAG_Byte(1),
        "Air": TAG_Short(300),
        "CanPickUpLoot": TAG_Byte(0),
        "AttackTime": TAG_Short(0),
        "IsBaby": TAG_Byte(1),
        "PersistenceRequired": TAG_Byte(0),
        "Fire": TAG_Short(-1),
        "FallDistance": TAG_Float(0.0),
        "Invulnerable": TAG_Byte(0),
        "EntityId": TAG_String(u'Zombie'),
      }),
    }),
  ]),
  "EntityId": TAG_String(u'Zombie'),
  "x": TAG_Int(44),
  "y": TAG_Int(10),
  "z": TAG_Int(-210),
})