We had this issue in my campaign. I thought that I had read somewhere that Fighting Defensively and Expertise (this was back in 3.0) could not be combined, and ruled it that way for a while. Then I came here for verification and found out I was wrong. They can be combined.
Sean K. Reynolds on his site had mentioned that he didn't think they should stack (because he saw them as two versions of the same thing,) which was where I'd gotten the idea from originally.