Why is Android Studio designer displaying my custom view nested inside itself, while it isn't

I've got a custom view for my app named AvatarView:

<?xml version="1.0" encoding="utf-8"?>
<com.ulouder.views.AdvancedRelativeLayout android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_gravity="center_horizontal"
    android:layout_margin="0dp"
    android:padding="0dp"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="CP"
        android:id="@+id/initialsView"
        android:layout_alignTop="@+id/avatarView"
        android:layout_alignLeft="@+id/avatarView"
        android:layout_alignBottom="@+id/avatarView"
        android:layout_alignRight="@+id/avatarView"
        android:background="@drawable/avatar_background"
        android:textColor="@color/white"
        android:gravity="center"
        android:textStyle="bold"
        android:textSize="8sp" />

    <com.makeramen.roundedimageview.RoundedImageView
        app:riv_coer_radius="20dp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/avatarView"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="4dp"
        android:layout_marginLeft="4dp"
        android:layout_marginBottom="4dp"
        app:riv_border_color="@color/lightGray"
        app:riv_border_width="0.2dp" />

</com.uLouder.views.AdvancedRelativeLayout>

AdvancedRelativeLayout is just a superclass of RelativeLayout with a small fix, nothing special there. Then, I've created a view that uses my custom view:

<?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">
<com.ulouder.views.AvatarView
    android:layout_width="50dp"
    android:layout_height="50dp"/>

</LinearLayout>

Nothing fancy either. But in the designer view of the second layout XML, I'm getting this:

The editor displays my view hierarchy like it has a nested instance of itself, while clearly there isn't. If I delete either one, they both get deleted. If I declare attributes on one of them, other also gets it. They are clearly the same instance. The only exception is setting an ID. Then the problem disappears, and only single instance is displayed as expected.

I've rebuilt the project, restarted Android Studio, but it's still the same. What am I doing wrong?