Android Firebase why do I get signed out after changing email?

Question

When the user wants to change his password, I prompt him with a Dialog to Re-authenticate. In this dialog, he can re-auth with password or via Google/Facebook. But when I update the firebase email, the user gets signed out and I want to avoid this. Consider this code:

private fun btnGoogle(){
    val acct = GoogleSignIn.getLastSignedInAccount(context)
    Timber.d(acct?.email)
    if (acct != null) {
        val credential = GoogleAuthProvider.getCredential(acct.idToken, null)
        auth(credential)
    }
}

private fun btnFacebook(){
    val token = AccessToken.getCurrentAccessToken()
    if(token!=null){
        val credential = FacebookAuthProvider.getCredential(token.token)
        auth(credential)
    }else{
        activity?.showBackgroundToast(getString(R.string.no_facebook_auth), Toast.LENGTH_LONG)
    }

}

private fun auth(credential: AuthCredential) {
    FirebaseAuth.getInstance().currentUser!!.reauthenticate(credential)
        .addOnFailureListener{e -> activity?.showBackgroundToast(e.localizedMessage, Toast.LENGTH_LONG)}
        .addOnCompleteListener { task ->
        if (task.isSuccessful) {
            mListener.onReAuthentication(true)
            dialog.dismiss()
        } else {
            activity?.showBackgroundToast(task.exception?.localizedMessage, Toast.LENGTH_LONG)
        }
    }
}

Then I call this function to actually update the email:

fun updateEmail(newEmail: String): Completable {
    return Completable.create { emitter ->
        val currentUser = FirebaseAuth.getInstance().currentUser
        currentUser!!.updateEmail(newEmail).addOnCompleteListener {
            if (it.isSuccessful) {
                Timber.d("updated email to %s", newEmail)
                emitter.onComplete()
            } else {
                emitter.onError(Throwable(it.exception?.localizedMessage))
            }
        }
    }
}

Everything works fine until I finally update the email. When I do, Firebase signs the user out every time!! (the following is from Android Studio logcat)

D/FirebaseAuth: Notifying id token listeners about a sign-out event.
D/FirebaseAuth: Notifying auth state listeners about a sign-out event.

It only happens when I change the email. Since I have an auth state listener, the user gets redirected to login screen after successfully updating the email, which makes no sense to me. Why? How can I avoid this?