why is form validation having issue with spaces?

[eluser]scout[/eluser]
I ended up hacking the system form_validation library by adding \s to the alpha_dash function. All the tests I ran against the server wouldn't reveal any server or configuration problems. This hack resolved the matter instantly. Still, on another server I did not have this problem. Weird.

Code:

function alpha_dash($str)
{
  return ( ! preg_match("/^([-a-z0-9_-\s])+$/i", $str)) ? FALSE : TRUE;
}