Haha for me it's the opposite. My password never works in Dropbox. I think it's because they don't support spaces in passwords, but they don't tell you when you change your password. They just accept the change and then you can't login.
There are many sites with little exceptions like that. I think that their password filter allows the characters, but their backend input sanitization doesn't, so it cleans it up and inserts a transformed version of the pass without providing notification. I've found this happens particularly often with passwords with symbols like !, #, or ;.
In general, this is one of the most frustrating things with trying to secure yourself online. I have gone through like "I WANT TO USE PASSPHRASES" then gone to places like PAYPAL and had them have an upper limit on password length. It's absurd that they all have slightly different requirements. I am switching to a password manager now.
This problem has been noted for some time. Past articles on the subject have shown how the various requirements for passwords come about through a combination of limitations imposed by the system they're being used on, or through misguided attempts at making things easier for users.
I wonder if there has ever been an attempt through a forum like RFCs or ISO to define a worldwide (or at least latin char set) standard for password requirements. Based on what i've seen in forums like this, there seems to be fairly broad acceptance that allowing a large number of characters from a character set with as few limitations as possible bests serves the interest of security. The thorniest issue would likely be about balancing requirements for increased complexity (eg capitals and lowercase, numbers, etc) with ease of use.
