SPF doesn't check the reply-to address, only that the host sending the mail is allowed to send mail for the domain in the MAIL FROM: header.

See: http://www.open-spf.org/FAQ/What_it_does/

Edit: for those unfamiliar with the intricacies of SMTP, the first three lines sent are HELO, MAIL FROM:, and RCPT TO:. The From: address that you see in your mail client is actually another header that gets sent once the server provisionally accepts the message based on the first three headers. It's the difference between the return address on the envelope of a paper letter, and an address printed on the letterhead of the actual letter.