I haven't seen anything quite like that before, but it looks to me like something gone awry with an email validation routine, which might be in Javascript if it's executed client-side before form submission. At least, that's where I would look first. Check also that the @ symbol is properly escaped: it has special-symbol use in multiple programming languages beyond Perl. I'd be curious to see what happens to underscores, hyphens, or other email address TLD's like in yahoo.com.tw.