Program: 177563
Project: 177563
Buggy source:
public void preSnapshot(){
  Set<Player> observerSnapshot=observers.get();
  Set<Player> observerLive=observers.getLive();
  Set<Entity> entitiesSnapshot=entities.get();
  Set<Entity> entitiesLive=entities.getLive();
  for (  Player p : observerSnapshot) {
    if (!observerLive.contains(p)) {
      for (      Entity e : entitiesSnapshot) {
        if (p.getEntity() != e) {
          NetworkSynchronizer n=p.getNetworkSynchronizer();
          if (n != null) {
            n.destroyEntity(e);
          }
        }
      }
    }
  }
  for (  Player p : observerLive) {
    if (!observerSnapshot.contains(p)) {
      for (      Entity e : entitiesSnapshot) {
        if (p.getEntity() != e) {
          NetworkSynchronizer n=p.getNetworkSynchronizer();
          if (n != null) {
            n.spawnEntity(e);
          }
        }
      }
    }
  }
  for (  Entity e : entitiesSnapshot) {
    if (!entitiesLive.contains(e)) {
      SpoutChunk newChunk=((SpoutChunk)e.getChunkLive());
      for (      Player p : observerLive) {
        if (!newChunk.observers.getLive().contains(p)) {
          if (p.getEntity() != e) {
            NetworkSynchronizer n=p.getNetworkSynchronizer();
            if (n != null) {
              n.destroyEntity(e);
            }
          }
        }
      }
    }
  }
  for (  Entity e : entitiesLive) {
    boolean justSpawned=((SpoutEntity)e).justSpawned();
    if (!entitiesSnapshot.contains(e) || ((SpoutEntity)e).justSpawned()) {
      SpoutChunk oldChunk=((SpoutChunk)e.getChunk());
      for (      Player p : observerLive) {
        if (!oldChunk.observers.get().contains(p) || justSpawned) {
          if (p.getEntity() != e) {
            NetworkSynchronizer n=p.getNetworkSynchronizer();
            if (n != null) {
              n.spawnEntity(e);
            }
          }
        }
      }
    }
  }
  for (  Entity e : entitiesLive) {
    for (    Player p : observerLive) {
      if (p.getEntity() != e) {
        NetworkSynchronizer n=p.getNetworkSynchronizer();
        if (n != null) {
          n.syncEntity(e);
        }
      }
    }
  }
}

Fixed version (ground truth):
public void preSnapshot(){
  Set<Player> observerSnapshot=observers.get();
  Set<Player> observerLive=observers.getLive();
  Set<Entity> entitiesSnapshot=entities.get();
  Set<Entity> entitiesLive=entities.getLive();
  for (  Player p : observerSnapshot) {
    if (!observerLive.contains(p)) {
      for (      Entity e : entitiesSnapshot) {
        if (p.getEntity() != e) {
          NetworkSynchronizer n=p.getNetworkSynchronizer();
          if (n != null) {
            n.destroyEntity(e);
          }
        }
      }
    }
  }
  for (  Player p : observerLive) {
    if (!observerSnapshot.contains(p)) {
      for (      Entity e : entitiesSnapshot) {
        if (p.getEntity() != e) {
          NetworkSynchronizer n=p.getNetworkSynchronizer();
          if (n != null) {
            n.spawnEntity(e);
          }
        }
      }
    }
  }
  for (  Entity e : entitiesSnapshot) {
    if (!entitiesLive.contains(e)) {
      SpoutChunk newChunk=((SpoutChunk)e.getChunkLive());
      for (      Player p : observerLive) {
        if (newChunk == null || !newChunk.observers.getLive().contains(p)) {
          if (p.getEntity() != e) {
            NetworkSynchronizer n=p.getNetworkSynchronizer();
            if (n != null) {
              n.destroyEntity(e);
            }
          }
        }
      }
    }
  }
  for (  Entity e : entitiesLive) {
    boolean justSpawned=((SpoutEntity)e).justSpawned();
    if (!entitiesSnapshot.contains(e) || ((SpoutEntity)e).justSpawned()) {
      SpoutChunk oldChunk=((SpoutChunk)e.getChunk());
      for (      Player p : observerLive) {
        if (justSpawned || oldChunk == null || !oldChunk.observers.get().contains(p)) {
          if (p.getEntity() != e) {
            NetworkSynchronizer n=p.getNetworkSynchronizer();
            if (n != null) {
              n.spawnEntity(e);
            }
          }
        }
      }
    }
  }
  for (  Entity e : entitiesLive) {
    for (    Player p : observerLive) {
      if (p.getEntity() != e) {
        NetworkSynchronizer n=p.getNetworkSynchronizer();
        if (n != null) {
          n.syncEntity(e);
        }
      }
    }
  }
}