It looks like you are doing everything correctly. My suspicion would be that part of your project is not being fully compiled afresh with the newly modified headers, so the second parameter to ReportFixture is not even being passed. That is, the calling code is still using the original single parameter version of the function, so childIndex is never pushed onto the callstack.
Are you using Xcode by any chance? Xcode is great at screwing this up when you have precompiled headers - it simply does not detect when they need refreshing. In addition to cleaning and rebuilding, you could try also deleting the 'derived data' - another wonderful idea from Apple that I'm sure is well intentioned, but the implementation seems rushed. Apparently, placing an option to delete the 'derived data' alongside the Build and Clean options would be too obvious, so you can find it hidden away in the Projects tab of the Organizer window. </rant>