MockMvc.perform throws an ConcurrentModificationException with parallel streams if MockHttpServletRequestBuilder cached

I'm writting some spring integration tests to test Spring Security in my application. I use RequestPostProcessor to create test users with different authorities. Also I cache them for reuse in all tests. See code below:

public final class Users {
    public static final RequestPostProcessor
        ANONYMOUS = anonymous();

    public static final RequestPostProcessor
        PERMISSIONS_READ = buildUser(Permissions.PERMISSIONS_READ);
    public static final RequestPostProcessor
        PERMISSIONS_WRITE = buildUser(Permissions.PERMISSIONS_WRITE);
    public static final RequestPostProcessor
        PERMISSIONS_DELETE = buildUser(Permissions.PERMISSIONS_DELETE);

    public static final RequestPostProcessor
        ROLES_READ = buildUser(Permissions.ROLES_READ);
    public static final RequestPostProcessor
        ROLES_WRITE = buildUser(Permissions.ROLES_WRITE);
    public static final RequestPostProcessor
        ROLES_DELETE = buildUser(Permissions.ROLES_DELETE);

    public static final RequestPostProcessor
        USERS_READ = buildUser(Permissions.USERS_READ);
    public static final RequestPostProcessor
        USERS_WRITE = buildUser(Permissions.USERS_WRITE);
    public static final RequestPostProcessor
        USERS_DELETE = buildUser(Permissions.USERS_DELETE);


    private Users() {}

    private static RequestPostProcessor buildUser(Permissions permission) {
        return buildUser(permission.toString(), permission.toString());
    }

    private static RequestPostProcessor buildUser(String name, String... authorities) {
        return user(name).authorities(SecurityUtils.authoritiesFromStrings(authorities));
    }
}

And when I use them in a test, I've got an ConcurrentModificationException.

Usage:

....................
@Autowired private WebApplicationContext context;
@Autowired private Filter springSecurityFilterChain;
MockMvc mvc = MockMvcBuilders
        .webAppContextSetup(context)
        .addFilters(springSecurityFilterChain)
        .build();
....................
MockHttpServletRequestBuilder req = get("some-url");
mvc.perform(req.with(Users.ANONYMOUS))
        .andExpect(status().isFound())
        .andExpect(header().string("Location", "login-url"));
Stream.of(Users.PERMISSIONS_WRITE, Users.PERMISSIONS_DELETE,
        Users.ROLES_WRITE, Users.ROLES_DELETE,
        Users.USERS_WRITE, Users.USERS_DELETE)
        .parallel()
        .forEach(Unchecked.consumer(user -> mvc.perform(req.with(user)) //Exception is here and caused by .with(user)
                .andExpect(status().isForbidden())));
....................

An exception:

....................
Caused by: java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
at java.util.ArrayList$Itr.next(ArrayList.java:851)
at org.springframework.test.web.servlet.request.MockHttpServletRequestBuilder.postProcessRequest(MockHttpServletRequestBuilder.java:754)
at org.springframework.test.web.servlet.MockMvc.perform(MockMvc.java:145)
at com.ipan.fin.man.integrational.PermissionsTest.lambda$checkReadSecurity$5(PermissionsTest.java:162)//line with my code
....................

Exception is thrown in org.springframework.test.web.servlet.request.MockHttpServletRequestBuilder because I'm caching it (MockHttpServletRequestBuilder req) and using in multiple streams. So, in case, when one stream iterate over postProcessors

@Override
public MockHttpServletRequest postProcessRequest(MockHttpServletRequest request) {
    for (RequestPostProcessor postProcessor : this.postProcessors) { //here
        request = postProcessor.postProcessRequest(request);
        if (request == null) {
            throw new IllegalStateException(
                    "Post-processor [" + postProcessor.getClass().getName() + "] returned null");
        }
    }
    return request;
}

And the second one adds new postProcessor to postProcessors

@Override
public MockHttpServletRequestBuilder with(RequestPostProcessor postProcessor) {
    Assert.notNull(postProcessor, "postProcessor is required");
    this.postProcessors.add(postProcessor); //here
    return this;
}

ConcurrentModificationException will be thrown.

As I understand in my code above it's not allowed to cache MockHttpServletRequestBuilder because of two reasons:

1. It's not thread safe
2. MockHttpServletRequestBuilder.with call adds new RequestPostProcessor, not replaces the old one as I expected.

Am I right?

P.S. With sequental streams the tests works fine and it looks like call of MockHttpServletRequestBuilder.with replaces the old RequestPostProcessor object, because I always get correct test result (response status from a server)