JIRA Integration: Inherited instance config do not allow enabling issues list at project level

Summary

When the JIRA integration is configured at the instance level, and Enable Jira issues is then enabled at the project level, the Enable Jira issues settings does not persist after clicking save.

Steps to reproduce

1. Enable JIRA Integration at the instance level under Admin - Settings - Integrations - JIRA
2. Go to any project, Enable Jira issues under Project - Settings - Integrations - JIRA
3. Save configs, page reloads
4. Enable Jira issues is back to its unchecked default

Example Project

What is the current bug behavior?

Changes to Enable Jira issues and other project-level overrides do not persist when JIRA settings are inherited from instance defaults.

What is the expected correct behavior?

Changes to Enable Jira issues and other project-level overrides should persist when JIRA settings are inherited from instance defaults.

Relevant logs and/or screenshots

Log in production_json when the save is performed:

{
    "method": "PUT",
    "path": "/hoth/sample-ci/-/services/jira",
    "format": "html",
    "controller": "Projects::ServicesController",
    "action": "update",
    "status": 302,
    "location": "https://URL/hoth/sample-ci/-/services/jira/edit",
    "time": "2021-04-07T12:46:21.698Z",
    "params": [
        {
            "key": "utf8",
            "value": "✓"
        },
        {
            "key": "_method",
            "value": "put"
        },
        {
            "key": "authenticity_token",
            "value": "[FILTERED]"
        },
        {
            "key": "service",
            "value": {
                "inherit_from_id": "2",
                "active": "true",
                "commit_events": "true",
                "merge_requests_events": "true",
                "comment_on_event_enabled": "true",
                "comment_detail": "standard",
                "url": "http://jira.example.com",
                "api_url": "",
                "username": "foobar",
                "password": "[FILTERED]",
                "jira_issue_transition_id": "",
                "issues_enabled": "true",
                "vulnerabilities_enabled": "false",
                "project_key": "[FILTERED]"
            }
        },
        {
            "key": "redirect_to",
            "value": "https://URL/hoth/sample-ci/-/settings/integrations"
        },
        {
            "key": "namespace_id",
            "value": "hoth"
        },
        {
            "key": "project_id",
            "value": "sample-ci"
        },
        {
            "key": "id",
            "value": "jira"
        }
    ],
    "remote_ip": "x.y.z.a",
    "user_id": 1,
    "username": "root",
    "correlation_id": "01F2P5X3X6WYZDHAPCDV7VH9WG",
    "meta.user": "root",
    "meta.project": "hoth/sample-ci",
    "meta.root_namespace": "hoth",
    "meta.caller_id": "Projects::ServicesController#update",
    "meta.feature_category": "integrations",
    "meta.client_id": "user/1",
    "redis_calls": 6,
    "redis_duration_s": 0.001564,
    "redis_read_bytes": 969,
    "redis_write_bytes": 1085,
    "redis_cache_calls": 5,
    "redis_cache_duration_s": 0.001253,
    "redis_cache_read_bytes": 610,
    "redis_cache_write_bytes": 389,
    "redis_shared_state_calls": 1,
    "redis_shared_state_duration_s": 0.000311,
    "redis_shared_state_read_bytes": 359,
    "redis_shared_state_write_bytes": 696,
    "db_count": 21,
    "db_write_count": 4,
    "db_cached_count": 1,
    "cpu_s": 0.070538,
    "mem_objects": 28295,
    "mem_bytes": 3455463,
    "mem_mallocs": 6883,
    "queue_duration_s": 0.016477,
    "db_duration_s": 0.0085,
    "view_duration_s": 0.0,
    "duration_s": 0.06257
}

Output of checks

Happens on self-managed instances, reported and reproduced on 13.10.0+

Results of GitLab environment info

Expand for output related to GitLab environment info

Premium customer ticket: https://gitlab.zendesk.com/agent/tickets/202845

Results of GitLab application Check

Expand for output related to the GitLab application check

Possible fixes

Workaround: Switch the project to use custom settings, and redefine all parameters. Now the settings persist, and remain persisted even if you switch back to defaults after.