title: ConstraintLayout issue on android 6
body: <p>I found a very strange bug using ConstraintLayout in my project. Indeed, this issue is only with android 6.</p>
  
  <p>I'm using the following XML to display a list of buttons for different login possibilities :</p>
  
  <pre><code>&lt;android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:fitsSystemWindows="true"
  tools:context="com.fagets.rainbowsixapp.login.LoginStepOneFragment"&gt;
  
  &lt;LinearLayout
      android:id="@+id/linearLayout_login_form"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:orientation="vertical"
      tools:layout_constraintRight_creator="1"
      tools:layout_constraintBottom_creator="1"
      android:layout_marginStart="65dp"
      app:layout_constraintBottom_toBottomOf="parent"
      android:layout_marginEnd="65dp"
      app:layout_constraintRight_toRightOf="parent"
      tools:layout_constraintLeft_creator="1"
      android:layout_marginBottom="18dp"
      app:layout_constraintLeft_toLeftOf="parent"
      android:layout_marginLeft="65dp"
      android:layout_marginRight="65dp"&gt;
  
      &lt;com.facebook.login.widget.LoginButton
          xmlns:facebook="http://schemas.android.com/apk/res-auto"
          android:id="@+id/login_button_facebook"
          style="@style/LoginButton"
          android:paddingTop="15dp"
          android:paddingBottom="15dp"
          facebook:com_facebook_login_text="@string/login_connect_facebook"/&gt;
  
      &lt;Button
          android:id="@+id/login_button_google"
          style="@style/LoginButton"
          android:textColor="@color/login_button_google_text"
          android:background="@drawable/login_button_shape_google"
          android:text="@string/login_connect_google"/&gt;
  
      &lt;Button
          android:id="@+id/login_button_anonymous"
          style="@style/LoginButton"
          android:background="@drawable/login_button_shape_anonymous"
          android:text="@string/login_connect_anonymous"/&gt;
  
      &lt;Button
          android:id="@+id/login_button_about"
          style="@style/LoginButton"
          android:background="@android:color/transparent"
          android:text="@string/login_connect_about"
          android:textColor="@color/login_button_google_text"/&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p></p>
  
  <p>My issue concern the <code>app:layout_constraintBottom_toBottomOf="parent"</code> in the LinearLayout. On Android 6 the LinearLayout is cropped instead of being stick to the bottom. It's correctly working on android 7, and even on android 4.4.2. Just after that, I tried to remove my LinearLayout to only use the ConstraintLayout, but I still have the same issue.</p>
  
  <p>Here is a screenshot on Android 7 :
  <a href="https://i.stack.imgur.com/WICPu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WICPu.png" alt="enter image description here"></a></p>
  
  <p>And here the issue with Android 6 :
  <a href="https://i.stack.imgur.com/N0vQM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/N0vQM.png" alt="enter image description here"></a></p>
  
  <p>Am I doing something wrong ? Or is it an issue with ConstraintLayout library ?</p>
  
  <p>Thanks !</p>