Heat Update Stack Preview result in misleading result

Steps to reproduce problem:
Step 1: Create stack using Template.yaml
Step 2: Update same stack which was created in step 1 using same Heat Template (Template.yaml)
Step 3: Stack update preview shows following result:

+-----------+------------------+--------------------+--------------------------------------------------------+
| state | resource_name | resource_type | resource_identity |
+-----------+------------------+--------------------+--------------------------------------------------------+
| unchanged | gpb_ext1_port | OS::Neutron::Port | { |
| | | | "stack_name": "forGovind", |
| | | | "stack_id": "6ae8c838-d943-4e7a-be83-0472d74ba2a6", |
| | | | "tenant": "68dee30f86344f14a650d0c75813801d", |
| | | | "path": "/resources/gpb_ext1_port" |
| | | | } |
| unchanged | volumegov | OS::Cinder::Volume | { |
| | | | "stack_name": "forGovind", |
| | | | "stack_id": "6ae8c838-d943-4e7a-be83-0472d74ba2a6", |
| | | | "tenant": "68dee30f86344f14a650d0c75813801d", |
| | | | "path": "/resources/volumegov" |
| | | | } |
| updated | instancegovmain- | OS::Nova::Server | { |
| | | | "stack_name": "forGovind", |
| | | | "stack_id": "6ae8c838-d943-4e7a-be83-0472d74ba2a6", |
| | | | "tenant": "68dee30f86344f14a650d0c75813801d", |
| | | | "path": "/resources/instancegovmain-" |
| | | | } |
+-----------+------------------+--------------------+--------------------------------------------------------+

I am wondering if i use the same template then why it is showing os::nova::server resource as updated ?

Please revert.

========================
Heat Template Content
File name : Template.yaml
========================

heat_template_version: 2013-05-23

resources:
  volumegov:
    properties:
      size: 1
    type: "OS::Cinder::Volume"

  gpb_ext1_port:
    type: OS::Neutron::Port
    properties:
      network: 551be7be-0386-447b-ba3b-91388a100c02

  instancegovmain-:
    properties:
      flavor: 205bb2df-d4fa-4478-bf97-cb2e69d440b5
      image: 26b9f717-137e-41e0-adbe-78346f72ba63
      networks:
        - port: { get_resource: gpb_ext1_port }
    type: "OS::Nova::Server"