Can't get value params[:model] first request?

I get nil from params[:model] in create action of my controller for the
first request when I start my mongrel server by using mongrel_rails
start. After that for second and third time are ok. In addition, if I
start my Mongrel by using script/server, it doesn’t have any problems at
all. It is different by starting mongrel server between script/server
and mongrel_rails start? Have you ever faced this problem?