xss filter bug?

[eluser]Base Willy[/eluser]
Looks like there is a bug in the xss filter.
I'm receiving an email address from the login form via $this->input->post('email', TRUE) and if there is a dot character in email - it turns empty after xss filtering For example on Gmail users could have emails with dot as id do.
Is it really a bug or i misunderstand something again?

[eluser]Base Willy[/eluser]
The question is so dumb or really no one knows the answer?