HAProxy track_script + nopreempt not working

I have 2 nodes with Keepalived v1.2.13, in Amazon AWS VPC.

I'm trying to achieve this scenario, assuming Node1 is MASTER:
If I stop HAProxy or stop keepalived or stop the node, failover to Node2.
If I start HAProxy back up on Node1 or start keepalived or start the node, do not failover to Node1 (no flapping).

With the following configuration, only by stopping keepalived or stopping the node, does the failover works. The priority change due to the track_script doesn't seem to affect the MASTER election.

Node1

vrrp_script chk_haproxy {       # Requires keepalived-1.1.13
script "killall -0 haproxy"     # cheaper than pidof
interval 2                      # check every 2 seconds
fall 2
weight 2                        # add 2 points of prio if OK
}

vrrp_instance VI_1 {
    advert_int 2
    state BACKUP
    nopreempt
    interface eth0
    virtual_router_id 51
    priority 101
    unicast_peer {
        172.17.16.10
    }

    notify_master "/etc/keepalived/randomscript.sh"
    track_script {
        chk_haproxy
    }
}

Node2

vrrp_script chk_haproxy {       # Requires keepalived-1.1.13
script "killall -0 haproxy"     # cheaper than pidof
interval 2                      # check every 2 seconds
fall 2
weight 2                        # add 2 points of prio if OK
}

vrrp_instance VI_1 {
    advert_int 2
    state BACKUP
    nopreempt
    interface eth0
    virtual_router_id 51
    priority 100
    unicast_peer {
        172.17.16.11
    }

    notify_master "/etc/keepalived/randomscript.sh"
    track_script {
        chk_haproxy
    }
}