[MaterialButton] Why Button rendering one more layer than TextView?

Description: Sorry, maybe it's not a bug, I just don't understand and couldn't find any clue to explain it.

I wrote a demo to illuminate it.

According to Official Site, here's the result.

So

• What causes this?
• Is there any way to avoid this overdraw?

Source code:

<com.google.android.material.button.MaterialButton
    android:id="@+id/btn"
    style="@style/Widget.MaterialComponents.Button.OutlinedButton"
    android:layout_width="wrap_content"
    android:background="@android:color/transparent"
    android:layout_height="wrap_content"
    android:layout_marginTop="30dp"
    android:text="@string/app_name"
    android:textAllCaps="false"
    app:iconPadding="0dp"
    app:iconSize="0dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<com.google.android.material.button.MaterialButton
    android:id="@+id/btn2"
    style="@style/Widget.MaterialComponents.Button.TextButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="12dp"
    android:background="@android:color/transparent"
    android:checkable="true"
    android:text="@string/app_name"
    android:textAllCaps="false"
    android:textColor="@android:color/white"
    app:iconPadding="0dp"
    app:iconSize="0dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@id/btn" />
<TextView
    android:id="@+id/btn3"
    android:paddingHorizontal="16dp"
    android:paddingVertical="8dp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:elevation="8dp"
    android:text="@string/app_name"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@id/btn2" />

Android API version: compileSdk 31

Material Library version: com.google.android.material:material:1.6.1

Device: Google Pixel 3 - Android 12

Inizia riproducendo la demo segnalata con Material Components 1.6.1 su Android 12/API 31, confrontando i due stili di MaterialButton con il TextView mentre la visualizzazione del GPU overdraw è abilitata. Esamina l'XML fornito e determina cosa causa il livello aggiuntivo e se la configurazione con sfondo trasparente può evitarlo; il lavoro è completato quando sono documentati la causa e un workaround supportato, se ne esiste uno.