So, up until now, I have been playing a completely pro-clean-hands, pro-ghost game. Well, until now. To show a friend the end of a mission, I reloaded the last save in the mission, played on through, and since once I had re-completed the mission I was back to about where I was before, I just saved over my last file, and got rid of auto-saves to make room. While I had gotten past the end of mission screen the previous time with no kills, a random civilian kill popped up. Now, I didn't play through enough to kill anyone, nor did I actually even draw my blade for almost all of what I played this second time.

Now, here's where that glitch in the title came into play. All of this was occurring at the Boyle's Party, and while following "Lady Boyle" into the cellar, I would randomly get spotted and the guards would go after me. I killed no one, bumped into no one, nothing. A few more tries and much aggravation later, I realized that every time It was these men in half red/half black masks. They would get suspicious, all of them in the room at the same time, and then shout for the guards. No other guests would react, just those angering men with the red and black masks. What I ended up doing was possessing one very fast, before they could raise alarm, and use them to ferry me a short distance into the kitchen/basemant, then leave them confused and head towards the cellar.

I did this both times, but this man was the only civilian I even came close to in the last play-through that ended up with me receiving a kill.

Is there any explanation for either of these weird glitches, and is there any way to get my one kill back and continue with my game without replaying the whole mission? (If I had to play it again, it would be my fourth time. I beat the game once, started again, then completed the mission not realizing shooting Lord Whats-his-face in that one duel for Pendleton counts as a kill, then played the mission again to get rid of that kill. Note that I shot him with a sleep dart the time I believe myself to have not killed anyone, and it didn't register as a kill when I got to the mission. Also note the fact he isn't a civilian either, he is counted as an enemy kill. I just really don't want to go through the hour long gameplay for a fourth time.)

I know this is a bit confusing, but thank you for your help.