Custom setter on subclassed PFObject property not working

Question

I have a subclasses PFObject - Conversation. I need a custom setter for it's users property.

So I changed @dynamic to @synthesize:

@synthesize users = _users;

And setup my setter as so:

-(void)setUsers:(NSArray *)users {
    @synchronized (self)
    {
        _users = users;
        self.numUsers = @(users.count);

        [self setReadWriteACLsForUsers:users];
    }
}

In my controller I set users:

self.conversation.users = users;

NSLog(@"self.conversation = %@",self.conversation);

I set breakpoints on the users setter and it seems to run through fine but in the log self.conversation the users property is nil.

---

EDIT

I changed my setter/getter to this:

 -(void)setUsers:(NSArray *)users {
        @synchronized (self)
        {
            [super setObject:users forKey:[Conversation usersKey]];
            self.numUsers = @(users.count);

            [self setReadWriteACLsForUsers:users];
        }
    }

- (NSArray *)users
{
    NSArray *ret = nil;

    @synchronized (self)
    {
        ret = [super objectForKey:[Conversation usersKey]];
    }
    return ret;
}

If I set breakpoints on the getter, ret has the correct values in them.

However, in this same conversation instance, in XCode it's showing nil for the two instance variables that I am setting up custom setters/getters for:

https://i.stack.imgur.com/a1dAL.jpg - I need 10 reputation to post images inline

So basically my synthesized instance variables aren't corresponding to the object keys in the PFObject and I don't know how to reconcile this.