My first guess would be that your mining contract expired at some point before that block was resolved and that at that point you went back to your regular mining pace. when the reward was computed on the massive loss of your mining power that those shares were not considered, and that the reward that you would have recieved (if the block had not gone invalid) was based on your lesser hashing rate that would have been brought back online when your contract expired. But this is only my opinion, and there are many more experienced miners on this thread that will surely chime in to correct me if necessary.