Yes, it has always behaved this way. You need a Joomla system plugin to redirect away from Joomlas user functions. CBSubs does this for you if the cbpaidsubsbot is installed, published, and public. Alternatively you can check Joomla.org for such a system plugin as believe there are a few available (unsure if any for J2.5). Another alternative is to just J2.5 built in redirect extension to setup redirects from Joomla user urls to CB urls.