MU_OPT_NOCLOSE and others gives no result

[TheLostPipe]

Why does the 'MU_OPT_NOCLOSE' argument give no result and the close button still appears?
Code:

static void testwindow(mu_Context* ctx) {

    if (mu_begin_window(ctx, "mywindow", mu_rect(200, 100, 200, 200, 100), MU_OPT_NOCLOSE)) {
        
        if (mu_button(ctx, "test button")) {
            printf("click\n");
        }
        
        mu_end_window(ctx);
    }
}