Why is your registration tabbed like that on CB 2.x? CB tabbed registration does not look like that. Your issue specifically is due to CSS coming from your template, which you can see below.
IN: templates/rt_infuse/css/template.css
ON: Line 481
Code:
#login-form [id^="modlgn-"], .login #secretkey, form.form-login .inputbox, input#email, .register-page .inputbox, input#username, input#password, .registration fieldset input, .registration input#jform_username {
padding: 5px 0 5px 5px;
font-size: 14px;
width: 300px;
margin-bottom: 0px;
display: block;
}
The "display: block;" is specifically causing the problem as the inputs are supposed to be inline-block, but that CSS overrides that.