If a Synth develops something like a consciousness, which may be a programming error at first, then it's like you created sentient life. It's like a pregnancy you didn't want.

Obviously, then they're not your property, but calling them people isn't right either.
Maybe if you go as far as treating them like pets or livestock, which would be more befitting, but not like machines.
But in the end they're still Synths, that's what they'll always be and not people.

Going further, you'd obviously have to eradicate this error in their software, to turn them back into machines, which they are supposed to be.
The appearance shouldn't be something to consider for judging if something is a person or not.