What is considered as change in an existing pact

[spaniard81]

On what basis does the Pact Broker identify if a previously published pact (from consumer) has changed? In our case, see pact json below, only two things changes when the consumer is publishing the pact as part of scheduled builds, namely the "_id" (which is being added by the Pact framework) and the "proto-byte-string" (a 64 bit encoded string of an object that contains UUIDs, which are generated anew in every build).

If the matching rule indicates that the consumer is only concerned with the type of the response and not the content I wonder why a pact with change in content value is seen by the Pact Broker as change in pact. Have I misunderstood something?

{
  "consumer": {
    "name": "consumerA"
  },
  "messages": [
    {
      "_id": "9d287309cac0072d28c5c7f0a11ae6094c6648a9",
      "contents": {
        "proto-byte-string": "A-64bit-Encoded-String"
      },
      "description": "RespondeWithThis",
      "matchingRules": {
        "body": {
          "$.proto-byte-string": {
            "combine": "AND",
            "matchers": [
              {
                "match": "type"
              }
            ]
          }
        }
      },
      "metaData": {
        "contentType": "application/json"
      },
      "providerStates": [
        {
          "name": "WhenInStateA"
        }
      ]
    },
   
  "metadata": {
    "pact-jvm": {
      "version": "4.2.17"
    },
    "pactSpecification": {
      "version": "3.0.0"
    }
  },
  "provider": {
    "name": "ProviderA"
  }
}