Microsoft Graph Calendar API All day event's start and end time are not obeying outlook.timezone

Question

Unable to get the start and end times for all day events in the preferer outlook.timezone.

I created an all day event for 7th October in GMT+5 time zone. The list and get methods of outlook calendar while using Prefer outlook.timezone is always returning the start and end times in GMT+5.

For example, this is the list method with Prefer = outlook.timezone="America/Los_Angeles":

    "value": [
        {
            "@odata.etag": "W/\"IloTFbAhCkiHTVTwnI2TXQABf0dkGw==\"",
            "id": "AQMkADI2ZDFmNDY4LTJlOWItNGVhOS1iM2E1LWZhMzg5ZDQ1MGUwNgBGAAADhQrIuhuED0_HAi76F3pFqAcAIloTFbAhCkiHTVTwnI2TXQAAAgENAAAAIloTFbAhCkiHTVTwnI2TXQABgAeCBwAAAA==",
            "createdDateTime": "2023-10-03T06:47:56.3712403Z",
            "lastModifiedDateTime": "2023-10-03T06:47:57.2702329Z",
            "changeKey": "IloTFbAhCkiHTVTwnI2TXQABf0dkGw==",
            "categories": [],
            "transactionId": 
            "originalStartTimeZone": "UTC",
            "originalEndTimeZone": "UTC",
            "start": {
                "dateTime": "2023-10-06T09:00:00.0000000",
                "timeZone": "America/Los_Angeles"
            },
            "end": {
                "dateTime": "2023-10-06T09:30:00.0000000",
                "timeZone": "America/Los_Angeles"
            },
        },
        {
            "@odata.etag": "W/\"IloTFbAhCkiHTVTwnI2TXQABf93HDQ==\"",
            "id": "AQMkADI2ZDFmNDY4LTJlOWItNGVhOS1iM2E1LWZhMzg5ZDQ1MGUwNgBGAAADhQrIuhuED0_HAi76F3pFqAcAIloTFbAhCkiHTVTwnI2TXQAAAgENAAAAIloTFbAhCkiHTVTwnI2TXQABgJ8E2gAAAA==",
            "createdDateTime": "2023-10-05T13:56:33.1916212Z",
            "lastModifiedDateTime": "2023-10-05T13:56:34.1370576Z",
            "reminderMinutesBeforeStart": 420,
            "isReminderOn": 
            "hasAttachments": 
            "subject": "all day event",
            "bodyPreview": "",
            "importance": "normal",
            "sensitivity": "normal",
            "isAllDay": 
            "isCancelled": 
            "isOrganizer": 
            "responseRequested": 
            "seriesMasterId": 
            "showAs": "busy",
            "type": "singleInstance",
            "body": {
                "contentType": "html",
                "content": ""
            },
            "start": {
                "dateTime": "2023-10-07T00:00:00.0000000",
                "timeZone": "America/Los_Angeles"
            },
            "end": {
                "dateTime": "2023-10-08T00:00:00.0000000",
                "timeZone": "America/Los_Angeles"
            },
        },
]

This is the same request using Prefer = outlook.timezone="UTC"

"@odata.context": "https://graph.microsoft.com/v1.0/$metadata#users('36e3c7fc-1c36-41a0-9545-fe8480386523')/calendar/calendarView",
    "value": [
        {
            "@odata.etag": "W/\"IloTFbAhCkiHTVTwnI2TXQABf0dkGw==\"",
            "id": "AQMkADI2ZDFmNDY4LTJlOWItNGVhOS1iM2E1LWZhMzg5ZDQ1MGUwNgBGAAADhQrIuhuED0_HAi76F3pFqAcAIloTFbAhCkiHTVTwnI2TXQAAAgENAAAAIloTFbAhCkiHTVTwnI2TXQABgAeCBwAAAA==",
            "createdDateTime": "2023-10-03T06:47:56.3712403Z",
            "lastModifiedDateTime": "2023-10-03T06:47:57.2702329Z",
            "changeKey": "IloTFbAhCkiHTVTwnI2TXQABf0dkGw==",
            "categories": [],
            "transactionId": 
            "originalStartTimeZone": "UTC",
            "originalEndTimeZone": "UTC",
            "start": {
                "dateTime": "2023-10-06T16:00:00.0000000",
                "timeZone": "UTC"
            },
            "end": {
                "dateTime": "2023-10-06T16:30:00.0000000",
                "timeZone": "UTC"
            },

        },
        {
            "@odata.etag": "W/\"IloTFbAhCkiHTVTwnI2TXQABf93HDQ==\"",
            "id": "AQMkADI2ZDFmNDY4LTJlOWItNGVhOS1iM2E1LWZhMzg5ZDQ1MGUwNgBGAAADhQrIuhuED0_HAi76F3pFqAcAIloTFbAhCkiHTVTwnI2TXQAAAgENAAAAIloTFbAhCkiHTVTwnI2TXQABgJ8E2gAAAA==",
            "createdDateTime": "2023-10-05T13:56:33.1916212Z",
            "lastModifiedDateTime": "2023-10-05T13:56:34.1370576Z",
            "originalStartTimeZone": "UTC",
            "originalEndTimeZone": "UTC",
            "reminderMinutesBeforeStart": 420,
            "isReminderOn": 
            "hasAttachments": 
            "subject": "all day event",
            "bodyPreview": "",
            "importance": "normal",
            "sensitivity": "normal",
            "isAllDay": 
            "isCancelled": 
            "isOrganizer": 
            "responseRequested": 
            "seriesMasterId": 
            "showAs": "busy",
            "type": "singleInstance",
            "start": {
                "dateTime": "2023-10-07T00:00:00.0000000",
                "timeZone": "UTC"
            },
            "end": {
                "dateTime": "2023-10-08T00:00:00.0000000",
                "timeZone": "UTC"
            },
        },

In each of the requests, the first event is a normal event. It obeys the Prefer outlook.timezone, but the second event which is an all-day event does not obey the preferred time zone. This is an important bug as I save the event and I don't know in which time zone I am receiving the events. I need to show these events to the users of my application in their time zone.

I tried using different timezones in the prefer header. The normal events timezone was changed but the all day events start and end times did not change