Multi Feature Instant Apps can't be proguarded?

By using Android Studio 3.0 Beta 5, using the default Project (Empty Activity) with Instant Apps on.

To turn on Proguard, I just set all the Build.Gradle (app, base and feature) with

debug {
   minifyEnabled true
   proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}

When compile the App works fine. However when compile the Instant Apps, it error out.

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.elyeproj.myapplication/com.elyeproj.myapplication.feature.MainActivity}: java.lang.ClassNotFoundException: could not find com.elyeproj.myapplication.feature.MainActivity in any atom class loader or parent class loader

It seems like the proguard just doesn't check the dependencies across features. How could this be solved?