s3api copy-object with --metadata-directive REPLACE appends the metadata instead of replacing it

[tonyipm]

Describe the bug
s3api copy-object with --metadata-directive REPLACE appends the object metadata instead of replacing it

To Reproduce
Create an s3 object 'a' in bucket 'ttt':
DEV03 [/mmfs1/data/TISRC] :>vgaws s3api put-object --bucket ttt --key a
{
"ETag": "d41d8cd98f00b204e9800998ecf8427e"
}

Use copy-object to add some metadata 'xxx=111':
DEV03 [/mmfs1/data/TISRC] :>vgaws s3api copy-object --bucket ttt --key a --copy-source ttt/a --metadata xxx=111 --metadata-directive REPLACE
{
"CopyObjectResult": {
"ETag": "d41d8cd98f00b204e9800998ecf8427e",
"LastModified": "2024-09-06T14:36:12.484700956+01:00"
}
}

Use head-object to display the metadata:
DEV03 [/mmfs1/data/TISRC] :>vgaws s3api head-object --bucket ttt --key a
{
"Restore": "",
"LastModified": "Fri, 06 Sep 2024 14:36:12 GMT",
"ContentLength": 0,
"ETag": "d41d8cd98f00b204e9800998ecf8427e",
"ContentType": "binary/octet-stream",
"Metadata": {
"xxx": "111"
},
"StorageClass": "STANDARD"
}

Repeat the copy-object with some different metadata yyy=222 using the REPLACE directive:
DEV03 [/mmfs1/data/TISRC] :>vgaws s3api copy-object --bucket ttt --key a --copy-source ttt/a --metadata yyy=222 --metadata-directive REPLACE
{
"CopyObjectResult": {
"ETag": "d41d8cd98f00b204e9800998ecf8427e",
"LastModified": "2024-09-06T14:36:12.484700956+01:00"
}
}

Now repeat the head-object, it shows both metadata keys:
DEV03 [/mmfs1/data/TISRC] :>vgaws s3api head-object --bucket ttt --key a
{
"Restore": "",
"LastModified": "Fri, 06 Sep 2024 14:36:12 GMT",
"ContentLength": 0,
"ETag": "d41d8cd98f00b204e9800998ecf8427e",
"ContentType": "binary/octet-stream",
"Metadata": {
"xxx": "111", ##<<<<<<<<<<<<<<<< WRONG
"yyy": "222"
},
"StorageClass": "STANDARD"
}

If you try this on AWS s3 then the second metadata update overwrites the first and so only the second one is seen (ie yyy=222, not xxx=111).

Expected behavior
copy-object using the metadata-directive REPLACE option should erase/overwrite any existing metadata and show only the latest, ie it should behave the same as AWS s3

Server Version
git clone from 6 sep 24

Additional context