I wanted to report an bug (I get an annoying "Welcome Message" each time I start editing a page and each time I submit the preview on pages and discussion pages).
In order to report that bug I tried to register my wikimedia account with phabricator. Since I have no e-mail address associated with my wikimedia account I invented a non-deliverable e-mail address in the phabricator registration form. There I am stuck and won't come out.