fontFamily not working as intended on API Level lower than 24

I'm facing a font rendering issue while using Fonts in XML

The following font family file is supposed to select roboto_regular font when used without android:textStyle attribute and roboto_medium when used with android:textStyle="bold" attribute:

roboto.xml

<font-family xmlns:app="http://schemas.android.com/apk/res-auto">
    <font
        app:font="@font/roboto_regular"
        app:fontWeight="400" />

    <font
        app:font="@font/roboto_medium"
        app:fontWeight="700" />
</font-family>

The layout applying this font family is:

<TextView
     android:id="@+id/textView"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:fontFamily="@font/roboto"
     android:text="Roboto font family"
     android:textSize="16sp" />

<TextView
     android:id="@+id/textView2"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:fontFamily="@font/roboto"
     android:text="Roboto font family bold"
     android:textSize="16sp"
     android:textStyle="bold" />

<TextView
     android:id="@+id/textView3"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:fontFamily="@font/roboto_regular"
     android:text="Roboto Regular"
     android:textSize="16sp" />

<TextView
     android:id="@+id/textView4"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:fontFamily="@font/roboto_medium"
     android:text="Roboto Medium"
     android:textSize="16sp" />

This is working as intended on Android 27 and 25, but an extra bold effect is applied on Android < 25 (see screenshots for Android 21 & 23).

API 27 rendering:

API 25 rendering:

API 23 rendering:

API 21 rendering:

The problem is more obvious when setting a different font for fontWeight="700" as seen in

custom_font_family.xml

<font-family xmlns:app="http://schemas.android.com/apk/res-auto">
    <font
        app:font="@font/roboto_regular"
        app:fontWeight="400" />

    <font
        app:font="@font/poor_story_regular"
        app:fontWeight="700" />
</font-family>

And the corresponding layout extract is:

<TextView
  android:id="@+id/textView5"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:fontFamily="@font/custom_font_family"
  android:text="Custom font family"
  android:textSize="16sp" />

<TextView
  android:id="@+id/textView6"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:fontFamily="@font/custom_font_family"
  android:text="Custom font family bold"
  android:textSize="16sp"
  android:textStyle="bold" />

<TextView
  android:id="@+id/textView7"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:fontFamily="@font/poor_story_regular"
  android:text="Poor story regular"
  android:textSize="16sp" />

<TextView
  android:id="@+id/textView8"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:fontFamily="@font/poor_story_regular"
  android:text="Poor story regular bold"
  android:textSize="16sp"
  android:textStyle="bold" />

A standalone project demonstrating the issue is available here: https://github.com/NicoEkino/FontFamilyIssue