In the account creation form the user must write the new username, the password (twice), and the CAPTCHA (the email address is not required). All of these are required, and if the form is submitted without any of them, it is reloaded and the fields that were already filled, must be filled again.
The "Go" button that exists on mobile phone touch keyboards submits the form even if the required fields aren't full yet. I saw people creating accounts and repeatedly tapping this button and getting their forms erased, and having to type the passwords, the email address, or the CAPTCHA yet again. This makes the process very confusing and frustrating.
To work around this, it's possible to tap the fields themselves one by one, but I know this because I'm an advanced user, and the account creation form is much more likely to be shown to new users, who may prefer the "Go" button.
The button should probably go to the next required field instead of submitting the form. Also, //not// deleting the values of sensibly filled fields would be great.