title: Subscription upgrade strange behaviour
body: <p>I have integrated google subscription in my app with few subscription based products.
  In my all products i have added 14 days free trial period.
  So now what making me feel strange is,
  First time user buys one subscription and starts his 14 days free trial period.Until this seems all fine.
  Now when i am trying to upgrade it with other subscription on the first day of free trial of old subscription it should give start date after old subscription's 14 days free trial.
  But its giving start date of next purchase after 8 days.
  I am not sure why its working like this.
  Any help will  be appreciated.</p>
  
  <pre><code>Bundle bundle=new Bundle();
              if(packageIdSKU.size() &gt; 0)bundle.putStringArrayList("skusToReplace",oldPackageId);
              Bundle buyIntentBundle = mService.getBuyIntentExtraParams(6, getPackageName(),
                      itemSku1, "subs", "bGoaXXXXXXX",bundle);
              PendingIntent pendingIntent = buyIntentBundle.getParcelable("BUY_INTENT");
              startIntentSenderForResult(pendingIntent.getIntentSender(),
                      1000, new Intent(), Integer.valueOf(0), Integer.valueOf(0),
                      Integer.valueOf(0));
  </code></pre>