Why does setting multiple fields in an UPDATE-SET statement for ONE QLDB document, return a list of the same document IDs?

When I run an UPDATE-SET statement against one of my documents in QLDB using this statement:

UPDATE Documents SET author = 'jkrowling', channel = 'dstv' WHERE docIdExt = 'newDocId'

The return value is a list of document IDs that were modified:

[
  {
    "documentId": "3Ax2GOnKEC82Qp5fwgPEBS"
  },
  {
    "documentId": "3Ax2GOnKEC82Qp5fwgPEBS"
  }
]

Why do I get a list of the same document IDs even if only one document was modified? I have noticed that the amount of IDs I get back is also directly related with the amount of SET elements in my query.

Expectation

Only to get a list of unique document IDs that were modified.

Result

Got a list duplicate document IDs that were modified.