Android RadiGroup allows multiple selection

Android API Level 24 (emulator) seems to allow multiple selection if I pre-select multiple RadioButton initially. I just want to know if this is a bug or not?

Here is the layout file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <RadioGroup
        android:id="@+id/radioGroup"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

       <RadioButton
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="@string/metal"
           android:checked="true"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/classical"
            android:checked="true"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/jazz"/>

    </RadioGroup>

</LinearLayout>

The app launches like this:

And if I click on Jazz, it becomes like this: