Why my scroll view does not scroll to the bottom when adding two sentences consecutively? - scrollview

Question

I created a scroll window like this, hoping it will auto scroll to the bottom when text continuously come:
public class LogWindow : MonoBehaviour
{
public Text logText;
Queue<string> textQueue = new Queue<string>();
public ScrollRect scrollRect;
public Scrollbar scrollbar;
void RefreshText()
{
string buffer = "";
foreach(string text in textQueue)
{
buffer += text;
buffer += '\n';
}
logText.text = buffer;
scrollRect.verticalNormalizedPosition = 0.0f;
scrollbar.value = 0.0f;
}
public void Log(string text, string color = "white")
{
text = String.Format("<color={0}>{1}</color>", color, text);
textQueue.Enqueue(text);
RefreshText();
}
}
It works fine when I call RefreshText once at a time. But when I do this:
Log("something 1");
Log("something 2");
I see that the log window is only scrolled down so that "something 1" is shown. I have to drag it manually to see "something 2".
My settings on the Text is:
I suppose there is something wrong in RefreshText. Can anyone tell me where did I go wrong?
Thank you!