sendDocument thumbnail parameter is not working correctly as per my expectation

[SpEcHiDe]

1. use sendDocument API with document and thumbnail parameter set.

curl -i "https://api.telegram.org/botTOKEN/sendDocument" -F "chat_id=CHAT_ID" -F "document=@file_example_WEBM_1920_3_7MB.webm" -F "[email protected]"

{
    "ok": true,
    "result": {
        "message_id": 1781334,
        "from": {},
        "chat": {},
        "date": 1724255401,
        "document": {
            "file_name": "file_example_WEBM_1920_3_7MB.webm",
            "mime_type": "video/webm",
            "thumbnail": {
                "file_id": "AAMCBQADGQMAARsuVmbGDKl90qUpBhvQ_OFUyK7u91A5AAIbEAACmTAxVmu7N9lyvqdpAQAHbQADNQQ",
                "file_unique_id": "AQADGxAAApkwMVZy",
                "file_size": 16541,
                "width": 320,
                "height": 320
            },
            "file_id": "BQACAgUAAxkDAAEbLlZmxgypfdKlKQYb0PzhVMiu7vdQOQACGxAAApkwMVZruzfZcr6naTUE",
            "file_unique_id": "AgADGxAAApkwMVY",
            "file_size": 3667214
        }
    }
}

curl -i "https://api.telegram.org/botTOKEN/sendDocument" -F "chat_id=CHAT_ID" -F "document=@sample_960x540.m4v" -F "[email protected]"

Actual Result

for WEBM documents, thumbnail is present in the sendDocument response, but absent in the original message which is verified by forwarding the media to Telegram JSON Bot.

WEBM document

M4V document

Expected Result

the thumbnail is set correctly on the media irrespective of the document passed to the API