Until Unity either addresses this issue (or redefines what "Transform" is or renames "NetworkTransform") here's a script that works for me:

using UnityEngine;
using UnityEngine.Networking;

/// <summary>
/// Fix so that localScale is also updated by NetworkTransform
/// </summary>
[RequireComponent(typeof(NetworkTransform))]
public class NetworkTransformScale : NetworkBehaviour {
[SyncVar]
Vector3 localScale;

void Start () {
UpdateLocalScale();
}

void Update () {
UpdateLocalScale();
}

void UpdateLocalScale() {
if (hasAuthority) {
localScale = transform.localScale;
} else {
transform.localScale = localScale;
}
}

override public int GetNetworkChannel() {
return GetComponent<NetworkTransform>().GetNetworkChannel();
}

override public float GetNetworkSendInterval() {
return GetComponent<NetworkTransform>().GetNetworkSendInterval();
}
}

It says a workaround is possible. Could someone enlighten me?