LinkedIn API session issue

Hi StackOverflow community

Our web app is built around Ruby on Rails 3. We use the linkedin rubygem to integrate the LinkedIn API.

We have successful Linkedin sign-in and registrations, but at rare cases (occurring twice or thrice a year so far), a user logins/registers via LinkedIn but a totally different and unconnected user shows up. (UserA enters LinkedIn credentials for the permissions, but some LinkedIn UserB gets returned). We don't get why this happens at all.

Here is the code snippet for the OAuth url:

 client = LinkedIn::Client.new('app_token', 'app_secret', @@config)
 request_token = client.request_token(:oauth_callback => "http://#{request.host}:#{request.port}/auth/oauth_account")
 session[:rtoken] = request_token.token
 session[:rsecret] = request_token.secret
 session[:provider_user] = "linkedin"
 redirect_to request_token.authorize_url

The bug highly makes it insecure for users. Could someone help?