Program: 33538
Project: 33538
Buggy source:
@SubscribeEvent public void onLivingTick(LivingUpdateEvent evt){
  JetpackParticleType jetpackState=null;
  ItemStack armor=evt.entityLiving.getEquipmentInSlot(3);
  boolean foundJetpack=false;
  if (armor != null && armor.getItem() instanceof ItemJetpack) {
    Jetpack jetpack=((ItemJetpack)armor.getItem()).getJetpack(armor);
    if (jetpack != null) {
      jetpackState=jetpack.particleToShow(armor,(ItemJetpack)armor.getItem(),evt.entityLiving);
      foundJetpack=true;
    }
  }
  if (jetpackState != lastJetpackState.get(evt.entityLiving.getEntityId())) {
    if (jetpackState == null) {
      lastJetpackState.remove(evt.entityLiving.getEntityId());
    }
 else {
      lastJetpackState.put(evt.entityLiving.getEntityId(),jetpackState);
    }
    PacketHandler.instance.sendToAllAround(new MessageJetpackSync(evt.entityLiving.getEntityId(),jetpackState != null ? jetpackState.ordinal() : -1),new TargetPoint(evt.entityLiving.dimension,evt.entityLiving.posX,evt.entityLiving.posY,evt.entityLiving.posZ,256));
  }
 else   if (foundJetpack && evt.entityLiving.worldObj.getTotalWorldTime() % 160L == 0) {
    PacketHandler.instance.sendToAllAround(new MessageJetpackSync(evt.entityLiving.getEntityId(),jetpackState != null ? jetpackState.ordinal() : -1),new TargetPoint(evt.entityLiving.dimension,evt.entityLiving.posX,evt.entityLiving.posY,evt.entityLiving.posZ,256));
  }
  if (evt.entityLiving.worldObj.getTotalWorldTime() % 200L == 0) {
    Iterator<Integer> itr=lastJetpackState.keySet().iterator();
    while (itr.hasNext()) {
      int entityId=itr.next();
      if (evt.entityLiving.worldObj.getEntityByID(entityId) == null) {
        itr.remove();
      }
    }
  }
}

Fixed version (ground truth):
@SubscribeEvent public void onLivingTick(LivingUpdateEvent evt){
  if (!evt.entityLiving.worldObj.isRemote) {
    JetpackParticleType jetpackState=null;
    ItemStack armor=evt.entityLiving.getEquipmentInSlot(3);
    boolean foundJetpack=false;
    if (armor != null && armor.getItem() instanceof ItemJetpack) {
      Jetpack jetpack=((ItemJetpack)armor.getItem()).getJetpack(armor);
      if (jetpack != null) {
        jetpackState=jetpack.particleToShow(armor,(ItemJetpack)armor.getItem(),evt.entityLiving);
        foundJetpack=true;
      }
    }
    if (jetpackState != lastJetpackState.get(evt.entityLiving.getEntityId())) {
      if (jetpackState == null) {
        lastJetpackState.remove(evt.entityLiving.getEntityId());
      }
 else {
        lastJetpackState.put(evt.entityLiving.getEntityId(),jetpackState);
      }
      PacketHandler.instance.sendToAllAround(new MessageJetpackSync(evt.entityLiving.getEntityId(),jetpackState != null ? jetpackState.ordinal() : -1),new TargetPoint(evt.entityLiving.dimension,evt.entityLiving.posX,evt.entityLiving.posY,evt.entityLiving.posZ,256));
    }
 else     if (foundJetpack && evt.entityLiving.worldObj.getTotalWorldTime() % 160L == 0) {
      PacketHandler.instance.sendToAllAround(new MessageJetpackSync(evt.entityLiving.getEntityId(),jetpackState != null ? jetpackState.ordinal() : -1),new TargetPoint(evt.entityLiving.dimension,evt.entityLiving.posX,evt.entityLiving.posY,evt.entityLiving.posZ,256));
    }
    if (evt.entityLiving.worldObj.getTotalWorldTime() % 200L == 0) {
      Iterator<Integer> itr=lastJetpackState.keySet().iterator();
      while (itr.hasNext()) {
        int entityId=itr.next();
        if (evt.entityLiving.worldObj.getEntityByID(entityId) == null) {
          itr.remove();
        }
      }
    }
  }
}