ConstraintLayout 1.1.0 views cannot reference each other on the same edge? - android-constraintlayout

Question

The following code used to work fine in 1.0.2, but does not work in 1.1.0 stable - literally removes the effect of every other constraint in all views in the layout. Is there a reason or is it just a quirk? Took a while to hunt it down.
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:app1="http://schemas.android.com/apk/res-auto">
<TextView
android:id="#+id/viewOne"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintBottom_toTopOf="#+id/viewTwo" <-- culprit
tools:text="View one"/>
<TextView
android:id="#+id/viewTwo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app1:layout_constraintTop_toBottomOf="#+id/viewOne" <-- culprit
tools:text="View two"/>
</android.support.constraint.ConstraintLayout>
Removing one of the culprit constraints brings everything back to normal in 1.1.0.

Answer 1

Add app:layout_constraintTop_toTopOf="parent" to viewOne and it will work again. You can also remove app:layout_constraintBottom_toTopOf="#+id/viewTwo" and nothing will change since it is not needed.
Although the two views are vertically constrained, they are constrained to one another and nothing ties them to the container. The group will slide to the top by default if not otherwise constrained. It look like both will slide to the top in 1.1.0 and line up one below the other in 1.0.2. This may be just a side effect of how the views are defined.
In any case, the XML is not well-formed and the views should all be constrained either directly or indirectly to the containing ConstraintLayout. Make the changes above and all will be well.

Answer 2

Just remove
app:layout_constraintBottom_toTopOf="#+id/viewTwo"
from the above xml code and you are good to go.
Below given is the code that works perfectly well.
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:app1="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/viewOne"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
tools:text="View one" />
<TextView
android:id="#+id/viewTwo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app1:layout_constraintTop_toBottomOf="#+id/viewOne"
tools:text="View two" />
</android.support.constraint.ConstraintLayout>
So in your case only
app:layout_constraintBottom_toTopOf="#+id/viewTwo" this is the culprit.