By default haproxy enables stateless SSL session resumption, but you can enable stateful session resumption in accordance with RFC 5077. This functionality, like the SSL handling it relies on is only available from haproxy 1.5.
The option to enable stateful SSL session resumption is as below
You will need to add it in to your bind line, like below
bind 0.0.0.0:443 ssl ... no-tls-tickets