singleTask launchMode in android not working

So, I have 4 activities Activity Activity1, Activity2, Activity3 and Activity4. I start from Activity1 then on some event I start Activity2 then on some event on Activity2 I start Activity3 as a new task as

public void onClick(View v) {
    Intent intent = new Intent(Activity2.this, Activity3.class);
    intent.setFlags(Intent.FLAG_ACTIVITY_MULTIPLE_TASK|Intent.FLAG_ACTIVITY_NEW_TASK);
    startActivity(intent);
}

Here Activity2 launchMode is decalared as singleTask.

Then I navigate from Activity3 to Activity4

When I start Activity2 from Activity4 I believe it should have backstack like

Task A

|Activity2|

|Activity1|

Task B

|Activity4|

|Activity3|

as shown in image below

but instead new instance of Activity2 is added to the current task as

Task B

|Activity2|

|Activity4|

|Activity3|

Task A

|Activity2|

|Activity1|

can someone please help me understand this?