Session destroyed after post from different ip

Hello.
My session gets destroyed when I send form using post method from website that is hosted on different ip. If I send it from other website with same ip or change method to get then session is not destroyed. Result is the same no matter on url destination.
Is it some kind of additional security protection or do I have some bug? I was trying to find the reason of this behavior but failed to do so.
I'm using version 4.1.1 with csrf disabled