My application stuck when I want to update firebase data

I’m trying to update multiple values in the firebase but I have small problem in the below code.
My application works fine in the first click on update button.
But when I click on update button again, I don’t know why the application stuck.

public list1: FirebaseListObservable<any[]>;
public list2: FirebaseListObservable<any[]>;

  this.list1.subscribe(dataX => {
    dataX.forEach(L1=> {
        this.list1.update(L1.$key, {
           title: title,
           desc: desc

Is there any help or other solution to solve my problem ?

I found the solution,

Its by using “take(1)