So while we were able to play splitscreen co-op using both of our profiles, none of my PDZ data was on hand, meaning that I headed into the final battle with a P9P and came out with "0" (how ironic) gamer points. The frustrating solution was to transfer K BROOKS's profile onto the Memory Unit, reattach my HDD, and beat the game again, so that we both received the points. Unfortunately, the gamer points problem persisted when we entered the "Combat Arena."
No big deal if you're not a sucker for gamer points, but this could pose a problem if you ever need to move the data to a different memory device. Let's hope Rare takes notice and issues a patch, and that other developers follow suit. [Note: we have not experienced nontransferable game data with any other 360 titles. Have you?]
Other Xbox 360 annoyances: 001, 002, 003, 004, 005, 006, 007, 008, 009, 010, 011, 012
Xbox 360 delights: 001, 002, 003, 004, 005, 006, 007