horizon: /accounts/{account_id} shows the ed25519_signed_payload signer type as unknown

[overcat]

What version are you using?

2.17.1-946a1d3f06d08bbe5c0df0afb0ae6bde43e1d079

What did you do?

Added a Signer(SIGNER_KEY_TYPE_ED25519_SIGNED_PAYLOAD) to the account via SetOptionsOp.
tx: https://horizon-testnet.stellar.org/transactions/3c38d8a6b546de3d27f3c1167835e06412dd7225585cec326afc89df97596cac

What did you expect to see?

https://horizon-testnet.stellar.org/accounts/GDXIZTYWWXRL5KB74ZOPZ5NHE5V6XNWHSOLAHMEKB6EJXMU4XHELQG7N
Account resp:

// ...
{
   "signers":[
      {
         "weight":1,
         "key":"GDXIZTYWWXRL5KB74ZOPZ5NHE5V6XNWHSOLAHMEKB6EJXMU4XHELQG7N",
         "type":"ed25519_public_key"
      },
      {
         "weight":10,
         "key":"PDSRX2P445WFOUMLIDMBBECMAQ2YARLOOQK44YNPBBGWR6LFY7A2YAAAAACWQZLMNRXQAAAARK3Q",
         "type":"unknown"
      }
   ],
}

What did you see instead?

Account resp:

// ...
{
   "signers":[
      {
         "weight": 1,
         "key": "GDXIZTYWWXRL5KB74ZOPZ5NHE5V6XNWHSOLAHMEKB6EJXMU4XHELQG7N",
         "type": "ed25519_public_key"
      },
      {
         "weight": 10,
         "key": "PDSRX2P445WFOUMLIDMBBECMAQ2YARLOOQK44YNPBBGWR6LFY7A2YAAAAACWQZLMNRXQAAAARK3Q",
         "type": "ed25519_signed_payload"
      }
   ],
}