When I have not been able to log-in, it was not a redirection problem. I got the login page, had some credentials to enter and a button to click. Either the button was not visible in the browser, clicking it had not result or clicking it had the wrong results. I changed microB settings to "allow pop-ups", which helped once, but not the other times.

My conclusion is that the html code of the login web page is buggy. In China, the problem may have been that microB did not support the right character encoding.

Of course, there are plenty of other login pages where I enter the credentials, click a button and it works.