Depending on when you played, it was probably a DoT effect on them. In early patches (and I'm not sure when this was changed, so that could be pre 1.6 or even pre 2.0) DoT effects would keep ticking and kill incapacitated enemies, but now all DoTs are non-lethal and stop when they go down.
Weird, I don't know what's happening then. I've been hitting them with all the quickhack DoTs and laying into them with a monowhip, and then just back off when they're down to a few percent at which point the bleed, burn, or poison incaps them. If you're using a blunt weapon be careful you're not hitting them after their health hits 0, because at that point any further damage will kill them, even nonlethal.
Depending on when you played, it was probably a DoT effect on them. In early patches (and I'm not sure when this was changed, so that could be pre 1.6 or even pre 2.0) DoT effects would keep ticking and kill incapacitated enemies, but now all DoTs are non-lethal and stop when they go down.
i'm on 2.0 but either way
Weird, I don't know what's happening then. I've been hitting them with all the quickhack DoTs and laying into them with a monowhip, and then just back off when they're down to a few percent at which point the bleed, burn, or poison incaps them. If you're using a blunt weapon be careful you're not hitting them after their health hits 0, because at that point any further damage will kill them, even nonlethal.