Expecting params hash but getting a string (Rails) -

i have typical signup form has, example, 3 fields: login, password, , email. we're using rails' form helpers, expecting these come in hash named user.

something close we'd expect:

parameters: {"action"=>"new", "controller"=>"users", "user"=>{"password"=>"[filtered]", "login"=>"new_user_login", "email"=>"new_user_email"}}

we stuff like: params[:user].merge(some_hash) # other stuff want save user object

a few times day we're getting "undefined method `merge' string", , looking @ requests, params instead coming in as:

parameters: {"action"=>"new", "controller"=>"users", "user"=>"login=new_user_login&email=new_user_email&password=[filtered]"}

params[:user], expect hash, coming in single query string, leading error.

has else seen in logs? it's coming same form others, , it's valid post authenticity_token set, etc. , looking login in our db, found user retried request , succeeded.

could @ fault of browser? individual firefox 3.6 on mac.