Maybe it's a funny glitch? The undead.
http://www.youtube.com/watch?v=ArXgZq4lbN8
If you want to save time, just watch from 01:50.
Also, please ignore the Chinese words in the video...for I once added explanations to upload it onto a Chinese website...Thanks XD
I wonder if you guys have ever met him...
It happened just as I was chased by a group of guards in Acre in the memory to kill Sibrand.
Three combo kills and several counter attacks cannot take him down...
At last he was killed by a counter kill of the hidden blade.
However, after that, my SSI didn't change until I ran to a hay stack.
(Which is not shown in the video. However you can judge it, for there is no sign of 'Reinitializing' and the music did't change after I finish the combat.)
I don't know why, but I wonder whether he is the person for Altair to eavesdrop.