I was playing through the Golden Cat mission and I decided to go the nonlethal way, I went and interrogated the painter and got out. As I was approaching the exit, I decided to rescue Emily. I did so, exited the Golden Cat, and then proceeded to meet e Slackjaw. I talked to him, gave him the combination for the painter's safe, and he shared the fate of the twins. As I got the alert that the Pendeltons were neutralized, suddenly Slackjaw became "alert" (the electricity bolts above his head, as seen with enemies) and the mission game over'd on me, the message said "You are enemies with the only man still able to eliminate the Pendeltons." I did NOT attack Slackjaw, in fact I had my weapons sheathed.
Could anyone help me out here? I really like this game but this glitch just ruins everything.
If anyone else encountered the same glitch, how'd you finish the mission?
Thanks and i'd really appreciate some help.

I had this glitch when I returned to Slackjaw with the safe combo--he went hostile halfway through his monologue. At first, I thought it was because he somehow knew that I had already emptied the safe.

I reloaded, and it worked normally the second time. Apparently a number of people have had a similar problem with him suddenly turning hostile. Just reload from the last autosave (entering the distillery) and try it again.

I had this problem too, and reloading the autosave didn't work either. Had to start over the mission from the beginning. Not sure how common it is, but so far it happened once of the 6 times I've played the mission.

Did you poison the elixir for Granny Rags in the prior mission and then release any weepers during the Golden Cat?

I've found him turn hostile in a similar situation some time after I opened one of the doors where the weepers were being held. The gang members get suspicious and it's possible for you to take the blame (even if you weren't directly seen letting them out).

I did in fact poison the elixir, but when I walked through the distillery no one was hostile. I didn't release the weepers, but I did see some of them walking around freely. I did everything Slackjaw told me to do and none of the gang members were hostile.
So do I repeat the the Campbell mission all over again!? I barely finished it, I had to go through a plethora of tasks and challenges just to finish it non-lethally.