iTunes Lookup API response is different for different clients

Right now it looks like a mystery. Please help me in solving it.

I use iTunes public API to fetch an album: "Metallica" by Metallica (see it in browser: US region, MV region). I construct the following URLs to fetch it via API:

US region https://itunes.apple.com/lookup?id=579372950&country=US&entity=album - works
MV region https://itunes.apple.com/lookup?id=579372950&country=MV&entity=album - doesn't work

Here's the actual behaviour I observe:

If I query GET https://itunes.apple.com/lookup?id=579372950&country=MV&entity=album in a Spring app (using RestTemplate + Jackson HttpMessageConverter) I get an empty response:
```
{
 "resultCount":0,
 "results": []
}
```
If I navigate to https://itunes.apple.com/lookup?id=579372950&country=MV&entity=album in a browser I get a file download prompt. The file contains an empty response:
```
{
 "resultCount":0,
 "results": []
}
```

If I query API using HttpPie http get https://itunes.apple.com/lookup?id=579372950&country=MV&entity=album I get a non-empty response !!!

{
    "resultCount": 1,
    "results": [
        {
            "amgArtistId": 4906,
            "artistId": 3996865,
            "artistName": "Metallica",
            "artistViewUrl": "https://music.apple.com/us/artist/metallica/3996865?uo=4",
            "artworkUrl100": "https://is1-ssl.mzstatic.com/image/thumb/Music/v4/0b/9c/d2/0b9cd2e7-6e76-8912-0357-14780cc2616a/source/100x100bb.jpg",
            "artworkUrl60": "https://is1-ssl.mzstatic.com/image/thumb/Music/v4/0b/9c/d2/0b9cd2e7-6e76-8912-0357-14780cc2616a/source/60x60bb.jpg",
            "collectionCensoredName": "Metallica",
            "collectionExplicitness": "notExplicit",
            "collectionId": 579372950,
            "collectionName": "Metallica",
            "collectionPrice": 9.99,
            "collectionType": "Album",
            "collectionViewUrl": "https://music.apple.com/us/album/metallica/579372950?uo=4",
            "copyright": "℗ 1991 Blackened Recordings",
            "country": "USA",
            "currency": "USD",
            "primaryGenreName": "Metal",
            "releaseDate": "1991-08-12T07:00:00Z",
            "trackCount": 13,
            "wrapperType": "collection"
        }
    ]
}

I tried it multiple times and the results seem to be consistent. I compared the requests and they seem to be identical.

Why does iTunes respond differently to different clients? I can't understand. What important detail am I missing?