I'm using 2.5.3 from 2009-09-18 and I have changed nothing that has to do with that section.
Only the mailtexts have been modified.
I can reproduce this bug everytime when I activate a user. But it is always "T" appearing, also if this is not in the username.
edit: Just tested unchanged 2.5.3 on MS SQL, all the buttons are without text and the links at the right have disappeared:
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Thanks for the quick change, but it is not correct yet.
Now there is the mail message including the password shown at the top.
I have changed /admin/user.php as you did.
edit: $message is already used for error messages, I have used $messagetext and it works now.
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