tx.Rollback() returns "op_response:0"

I have the following table created:

CREATE TABLE my_table (
  id  INTEGER NOT NULL
  key VARCHAR(64) NOT NULL
  value VARCHAR(64)
);

Respectively in go:

// db.go
package utils
import (
    "database/sql"
    _ "github.com/nakagami/firebirdsql"
    "log"
)

var DB *sql.DB

func InitDB(dataSourceName string) {
    var err error
    DB, err = sql.Open("firebirdsql", dataSourceName)
    if err != nil {
        log.Panic(err)
    }

    if err = DB.Ping(); err != nil {
        log.Panic(err)
    }
}

//main.go
package main

import (
    "log"
    "test/utils"
    "database/sql"
)

utils.InitDB("sysdba:masterkey@127.0.0.1/TEST")

trans, err := utils.DB.Begin()
if err != nil {
    log.Println(err)
}
var rowId = sql.NullInt64{}

err = trans.QueryRow(
    "INSERT INTO my_table (id, key, value) VALUES (?, ?, ?) RETURNING id",
    1, "testKey", "testValue").
    Scan(&rowId)

if (err != nil) || (!rowId.Valid) || (rowId.Int64 <= 0) {
    log.Println(err)
    err = trans.Rollback()  // returns "op_response:0"
    if err != nil {
        log.Println(err.Error())
    }
} else {
       trans.Commit()
}

If correct values are passed as arguments to tx.QueryRow, everything is ok and the query is committed correctly.
If for some reason the query fails (eg if invalid arguments are passed), tx.QueryRow returns an error - thats normal. But after if I try to rollback the transaction - it also fails with an error message "op_return:0". The more frustrating is that each next call to DB.Begin() returns the same transaction.

I tried x86,x64 versions of Firebird 2.5, different ways to execute the query - via stored procedure; just a tx.Execute() without a returning clause.

nakagami / firebirdsql

tx.Rollback() returns "op_response:0" #38