Http Compression Stats NULL even it works perfectly. (Version 13 no HF)

I am doing some tests and i have a vm appliance with 45 day lab license. I choose default httpcompression profile on a vserver and tested it with ;

with ; curl https://192.168.110.222/x.html -k -H 'Accept-Encoding: gzip,deflate' -I
and with ; curl https://192.168.110.222/x.html -k -I

I clearly see response vary header and size changes which confirms the compresion is working perfectly.

The problem is there is no global statistics shows regarding compression. It shows 0 and not changes on gui, on cmd line tmsh and on snmp requests