Hi Atheling,
I do have 2 domains on my box – but this should no be a problem isn’t it?
How did you configured the SPF with only one txt entry? As far as I understood there should be two entries for this : one txt and one spf.
Have you test your domain spf entries with tools like:
http://www.politemail.com/check-spf.aspx
Regards,
somleac