I use KeePass as my password manager and whenever I can I use a randomly-generated 55-character password with a mix of uppercase letters, lowercase letters, numbers, special characters, brackets, underscores, and dashes. I created a password matching that criteria for TM3. When I originally set up my account, the forum software logged me in automagically, so I didn't need to actually enter my password, and since that point, there's been a cookie set that remembers my login details every time I visit.
However, I just tried to log in using that same password on another PC, and it appears that vBulletin invisibly trimmed 5 characters off my password when it was originally set. So what I have in my password manager is 55 characters, while what vBulletin has is 50 characters, and I can't log in because my password is "wrong."
Not sure if this is addressed in a newer version of vBulletin anywhere, but it should probably be noted somewhere in the signup process if not.