I am probably missing something, but it seems to me, that it's currently kind of a hassle to stay logged in the forum. When you click on "Login" you are sent to Uber's global Login form ( https://uberent.com/user/login?titleId= ... Login=true ). However, there is no option to stay logged in to the forum. The only other way to log in to the forum and stay logged in, that I can see currently, is to subscribe to a thread, wait for a reply notification mail and click the link to view the newest post, which looks something like viewtopic.php?f=1&t=123&p=1234&e=12345 for instance. If you are currently logged out, this will send you to the phpBB normal log-in form, where you have the option to stay logged in. Isn't there a better way?
I just have this: http://forums.uberent.com/forums/viewforum.php?f=1 bookmarked and have no such problem. I've only seen the page in your link when I initially tried to log in from my phone which kept failing even with correct password etc.
That's just the forum overview, it has no influence on whether or not you are logged in and how you get logged in. You have no problems, because you already have your log-in cookie set. It won't matter to you then, if you visit that page first, or any other page on the forum. Click "Logout [...]" in the top right corner and then "Login" again. You should be directed to that page. phpBB's own login form only comes up in the aforementioned case, or if you try to reply to a post while being logged out for instance.
Yeah, as I said, you are presented with phpBB's own log-in form, if you try to do stuff like that, you just don't have the option via Uber's global login. Well, it's not really removed, it's still there, just not via Uber's global login.