Trying to reproduce this on my 4.2.2 (v17) Nexus 4. Added this drawable:

<transition xmlns:android="http://schemas.android.com/apk/res/android" >
    <item android:drawable="@drawable/test_drawable_blue"/>
    <item android:drawable="@drawable/test_drawable_green"/>
</transition>

where blue/green drawables look like this:

<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <size
        android:width="@dimen/drawable_large_size"
        android:height="@dimen/drawable_small_size" />
    <solid
        android:color="@color/test_blue" />
</shape>

Then added this test:

    @Test
    public void testMutateTransitionDrawable() {
        Drawable drawable = ResourcesCompat.getDrawable(mResources,
                R.drawable.test_transition_drawable, null);
        assertTrue(drawable instanceof TransitionDrawable);

        Drawable mutated = drawable.mutate();
        assertTrue(drawable instanceof TransitionDrawable);
        assertTrue(mutated instanceof TransitionDrawable);
    }

It passes on the device. Going to also try on other earlier devices a bit later in the day once they are charged.

Also not reproducible on Galaxy Nexus running 4.0.1 (v14), 4.0.4 (v15) and 4.2.2 (v17)

https://android-review.googlesource.com/c/platform/frameworks/support/+/960032 with the test. Closing as not reproducible. If this is still happening for you, we'd need to see either a test (same as in this CL) or a small, standalone sample project that reproduces this issue on v17 (or other) devices.