Somebody is trying to outshine Mt. Gox in terms of amateurism. I wouldn't be surprised to find a number of other vulnerabilities (SQL injection ?). Who the hell thinks it's OK to store non-encrypted passwords in this day and age? It's not like you don't have a major security breach every month... Also, I like the 'handler.php' endpoint returning some kind of ugly pseudo-SOAP. Ugh.
" Who the hell thinks it's OK to store non-encrypted passwords in this day and age?" You'd be surprised: http://plaintextoffenders.com/ ...and an amazing number of finance organisations who can't handle non alpha-numeric characters in passwords, indicating failure to hash.
Or they want to avoid the customer service calls "I am in Russia and use a Euro sign in my password, how do I login?!?!?!"/"Help, I have a Macbook from my brother, where is the vertical pipe (|) symbol?" so they restrict the keyspace to azAZ09 for reducing this type of error.