kerio vpn service strange internet use

I use kerio vpn service to bypass govemental restrictions on the net. Recently I noticed an unusual inteet usage, which is, given the high price of d/u traffic in our country, a real trouble. I carried out serveral download tests with and without vpn coection and the result is that the data transferred when kerio service is on, is at least twice as much as transferred when it's off.

Any idea?