Problem

The RPC returns empty arrays for pre/postTokenBalances for the transaction below, while there is actually a token transfer.

https://explorer.solana.com/tx/2M8DiyZuMwgJRXtccpj3VbQ4t7AFnSHfr7EFbq7dtEdhhguXGVofHb2DSx626PnByNTihcfLKhZ6xviGzcXGvJo6

Expected: pre/postTokenBalances should have the records for 2432558691285.5888 KIN transferred.

Actual: pre/postTokenBalances are just empty arrays.

According to the RPC documentation:

preTokenBalances: <array|undefined> - List of token balances from before the transaction was processed or omitted if token balance recording was not yet enabled during this transaction

• I assume "omitted" here means undefined. For this transaction, I'm getting empty array and not undefined, which means "token balance recording" is enabled for this transaction?
• How do I know whether a transaction has "token balance recording" enabled? Tried searching around, but couldn't find any relevant info.

RPC response snippet:

{
    "jsonrpc": "2.0",
    "result": {
        "blockTime": 1608579465,
        "meta": {
            "err": null,
            "fee": 10000,
            "innerInstructions": [],
            "logMessages": [
                "Program TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA invoke [1]",
                "Program log: Instruction: TransferChecked",
                "Program TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA consumed 5651 of 200000 compute units",
                "Program TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA success"
            ],
            "postBalances": [
                9690639800680,
                0,
                2039280,
                2039280,
                1461600,
                1118555520
            ],
            "postTokenBalances": [],
            "preBalances": [
                9690639810680,
                0,
                2039280,
                2039280,
                1461600,
                1118555520
            ],
            "preTokenBalances": [],
            "rewards": [],
            "status": {
                "Ok": null
            }
        },
        "slot": 56619660,
        "transaction": {
            "message": {
                "accountKeys": [
                    {
                        "pubkey": "agsWhfJ5PPGjmzMieWY8BR5o1XRVszUBQ5uFz4CtDiJ",
                        "signer": true,
                        "source": "transaction",
                        "writable": true
                    },
                    {
                        "pubkey": "agmTGWQdxedymuZ1XzWSTPxXyCRDG93RBXmKHgw6AMm",
                        "signer": true,
                        "source": "transaction",
                        "writable": false
                    },
                    {
                        "pubkey": "mintUWJmhmFHzZnw5SRE3CEx72ib9CZYJrrzHzZzWj3",
                        "signer": false,
                        "source": "transaction",
                        "writable": true
                    },
                    {
                        "pubkey": "5CtDePTpEadRxUk6pkFVmShGMpgjvwVw6eBTcpZedkQS",
                        "signer": false,
                        "source": "transaction",
                        "writable": true
                    },
                    {
                        "pubkey": "kinXdEcpDQeHPEuQnqmUgtYykqKGVFq6CeVX5iAHJq6",
                        "signer": false,
                        "source": "transaction",
                        "writable": false
                    },
                    {
                        "pubkey": "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA",
                        "signer": false,
                        "source": "transaction",
                        "writable": false
                    }
                ],
                "addressTableLookups": null,
                "instructions": [
                    {
                        "parsed": {
                            "info": {
                                "authority": "agmTGWQdxedymuZ1XzWSTPxXyCRDG93RBXmKHgw6AMm",
                                "destination": "5CtDePTpEadRxUk6pkFVmShGMpgjvwVw6eBTcpZedkQS",
                                "mint": "kinXdEcpDQeHPEuQnqmUgtYykqKGVFq6CeVX5iAHJq6",
                                "source": "mintUWJmhmFHzZnw5SRE3CEx72ib9CZYJrrzHzZzWj3",
                                "tokenAmount": {
                                    "amount": "243255869128558880",
                                    "decimals": 5,
                                    "uiAmount": 2432558691285.589,
                                    "uiAmountString": "2432558691285.5888"
                                }
                            },
                            "type": "transferChecked"
                        },
                        "program": "spl-token",
                        "programId": "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA"
                    }
                ],
                "recentBlockhash": "8ddxF1eMK5cnTuqJpmQUmAcBh6RNpjev5ebFM7JQUJKg"
            },
            "signatures": [
                "2M8DiyZuMwgJRXtccpj3VbQ4t7AFnSHfr7EFbq7dtEdhhguXGVofHb2DSx626PnByNTihcfLKhZ6xviGzcXGvJo6",
                "55EZawMh8Kj4agKBksE5FHHvCQ4q3qbUYu8ACrYuyBS7styWpcGXeaUspRrYsmTVreBoFUk1epdmAKa72wKUdSqS"
            ]
        },
        "version": "legacy"
    },
    "id": "b7049b7f-e293-4ddc-8ce7-29b4e0cbd508"
}

Proposed Solution

Either:

• Reflect the token transfer in pre/postTokenBalances for the above transaction, or
• If this is related to "token balance recording" not being enabled for the transaction, update the documentation to clearly explain it.