HI,
I dont know if it is nginx related or not, but i give a try here.

we have a setup of nginx+php-fpm for cs cart shopping software.
everything is works fine but one big problem.
users can not login in all browsers except firefox.

and the problem is because of some cookies dont save in browsers.
the only browser that save cookie is firefox and other browsers dont save needed cookie.

is there any thing related to nginx ?? or it is php-fpm problem ?

by the way we have cscart installed on IIS6 and also IIS7 and everything is OK and works fine in all browsers.

regards