Linktransformer not working on page reload

I've an application with a link transformer that worked perfectly in AEM 5.6.1. After putting the code on a AEM 6.1 instance, the link transformer works only partly. On opening the page for the first time, it is transformed, it is a login page and there is validation. so a servervalidation.jsp is called and that produced an error(username or password not correct). The page is reloaded including the messages, but not the link transformer is not called resulting in a incorrect page.

An addition, it looks like it fails because it is a POST method

Anybody any ideas ?