JTD fails validation of discriminated union

[ioder]

What version of Ajv are you using? Does the issue happen if you use the latest version?
8.11.0

Ajv options object

{}

JSON Schema

{
    "discriminator": "dicriminatorProperty",
    "mapping": {
        "manual": {
            "properties": {
                "first": { "type": "uint16" },
                "second": { "type": "uint16" },
                "third": { "type": "uint16" },
                "fourth": { "type": "uint16" },
                "fifth": { "type": "uint16" },
                "sixth": { "type": "uint16" },
                "additionalOne": { "type": "uint16" },
                "additionalTwo": { "type": "uint16" }
            }
        },
        "auto": {
            "properties": {
                "first": { "type": "uint16" },
                "second": { "type": "uint16" },
                "third": { "type": "uint16" },
                "fourth": { "type": "uint16" },
                "fifth": { "type": "uint16" },
                "sixth": { "type": "uint16" },
                "additionalThree": { "type": "uint16" }
            }
        }
    }
}

Sample data

 {
      "dicriminatorProperty": "manual",
      "first": 17,
      "second": 17,
      "third": 17,
      "fourth": 17,
      "fifth": 17,
      "sixth": 17,
      "additionalOne": 17,
      "additionalTwo": 17
}

Your code

const commonProperties = {
    first: { type: "uint16" },
    second: { type: "uint16" },
    third: { type: "uint16" },
    fourth: { type: "uint16" },
    fifth: { type: "uint16" },
    sixth: { type: "uint16" }
};

const schema = {
    discriminator: "dicriminatorProperty",
    mapping: {
        manual: {
            properties: {
                ...commonProperties,
                additionalOne: { type: "uint16" },
                additionalTwo: { type: "uint16" }
            }
        },
        auto: {
            properties: {
                ...commonProperties,
                additionalThree: { type: "uint16" }
            }
        }
    }
};

const Ajv = require("ajv/dist/jtd");
const ajv = new Ajv();
const validate = ajv.compile(schema);

const data1 = {
    dicriminatorProperty: "manual",
    first: 17,
    second: 17,
    third: 17,
    fourth: 17,
    fifth: 17,
    sixth: 17,
    additionalOne: 17,
    additionalTwo: 17
};

const data2 = {
    dicriminatorProperty: "auto",
    first: 17,
    second: 17,
    third: 17,
    fourth: 17,
    fifth: 17,
    sixth: 17,
    additionalThree: 17
};

// ---------------------------------------------------
// This validation passes
// ---------------------------------------------------
console.log("Valid data1? ", validate(data1));

// ---------------------------------------------------
// This validation fails
// ---------------------------------------------------
console.log("Valid data2? ", validate(data2));

Validation result, data AFTER validation, error messages

{
    instancePath: "/dicriminatorProperty",
    schemaPath: "/mapping/manual",
    keyword: "properties",
    params: {
         error: "additional",
         additionalProperty: "dicriminatorProperty"
    },
    message: "must NOT have additional properties"
}

What results did you expect?
The number of properties in the object seems to be affecting the validation result. This should not happen and discriminator should not be recognised as an additional property.

Are you going to resolve the issue?
Resolution of this issue is non actionable by me

[epoberezkin]

not reproducible on smaller example: https://runkit.com/esp/637163192eb1b90008da2666

seems to need exactly that number of properties, for me data1 fails that has more properties, data2 passes.