Battle.Net App Password Input

After several test runs, I have found that all Blizzard services (Website, Forums, Store, & Desktop App) will allow you to enter any password longer than 16 characters and still log in. So long as the first 16 characters are the correct string.

For clarification, the maximum password length is 16 characters.
An example password being: PasswordPassword

However, I can enter passwords beyond 16 characters:
Example: PasswordPassword123
Example: PasswordPasswordasdf
etc…

and still be able to log in because the first 16 are correct. Shouldn’t this return an invalid password error? Or at least stop allowing input beyond 16 characters?