It would make sense for the signing bonus now to stretch out for another season since his contract, in essence, extends for one more year. Otherwise, for 2014, none of his signing bonus would count against the cap as it would have all lapsed.
With that said, I have no clue the NFL's salary cap rule on this. I guess if someone knows what the cap hit was for Vick (prior to release) when he was indefinitely suspended, then we might have a better idea. I know Loomis and the Saints know though... and that's good enough for me.