all the kittens ive ever raised from too young (under 6 weeks) tend to become stranger agressive and dont have the same "inhibitions" as one raised with its littermates.
our current cat pippin i found at 4 weeks old, i weaned him myself and for the first few months he was fine, took him for his neuter he tried to eat the vet (32 stitches in his arm later and a gas box to knock the tiny 5 month olf kitten out to neuter him) he was growling and i have had to do shots myself since..
since that point he has bonded strongly with my sister and my mother and the cocker charlie but attacks visiously anyone else.
my friends found a little 2 week old kittne and hand reared it, they named it malar (for those familiar with forgotten relms...yeah..."mal" is a chaos demon in a grey coat, his lack of mother and siblings to leanr from hes the same way, hes bonded with his "mommy" but will attack anyone else...hes semi playfull about it wiht him its as if he never learnt how hard is to hard and when to stop.