RestTemplateBuilder setConnectTimeout not working

When I use auto-configured bean of RestTemplateBuilder, the timeout field doesn't set as intended.

code:

    public WebHookService(RestTemplateBuilder restTemplateBuilder) {
        restTemplate = restTemplateBuilder
                .setConnectTimeout(Duration.ofSeconds(10))
                .setReadTimeout(Duration.ofSeconds(30))
                .build();

Result:

However When I set the custom bean of RestTemplateBuilder, timeout is set as Intended.

code:

    @Bean
    RestTemplateBuilder restTemplateBuilder() {
        return new RestTemplateBuilder();
    }
 
    // ...

    public WebHookService(RestTemplateBuilder restTemplateBuilder) {
        restTemplate = restTemplateBuilder
                .setConnectTimeout(Duration.ofSeconds(10))
                .setReadTimeout(Duration.ofSeconds(30))
                .build();

Result:

As far as I know, In Spring Boot 1.4.0 application RestTemplateBuilder is available as a bean and you can simply use that.
So there should be no difference between using custom bean and auto-configured bean.
... But it didn't!

Anyone who knows why?