Google Play Developer API: “startTimeMillis” is updated when it should not

[BlindOSX]

I am developing an application with in-app subscriptions. On our servers, I check the validity of each subscription through the Google Play Developer API.

As stated in the docs, a request to the Purchases.subscriptions endpoint, returns something like that:

{
  "kind": "androidpublisher#subscriptionPurchase",
  "startTimeMillis": long,
  "expiryTimeMillis": long,
  "autoRenewing": boolean
}

However, I am finding some strange behavior with it. When a user cancels a subscription through Google Play app, the "startTimeMillis" field is updated to the time of cancellation.

According to the documentation, "startTimeMillis" is "Time at which the subscription was granted", so I expected that this value should not change. Could anybody explain me why it is updated after a cancellation?

I have another important question that I can not test yet... Could someone, who has spent several months working with subscriptions, tell me if this "startTimeMillis" is updated too when the subscription is automatically renewed? I expect too that this should not change but... now, I am not sure about this.

Thank you

P.S: Same issue on StackOverflow