Copy-chunk on streams is currently not supported. We actually end up doing a copy in the data stream (!) and the copy-chunk on the stream returns success.
Subsequently the client calls setinfo(size) on the stream which acutally creates the stream with the correct size but filled with 0 bytes.
Voila, unnoticed data corruption. Though the user might notice that the macOS metadata is somehow broken, eg Finder tags are lost.
Patches in master -7 9d30d47b1ec33c815d204198952bf597cd602b49 and in 4.7 and 4.8.