Clojurians Log v2

I keep getting a ConcurrentModificationException java.util.HashMap$HashIterator.nextNode (:-1) every second time I restart my http-kit webserver with mount. The server defstate looks like this:

(mount/defstate webserver
  :start (do
           (log/info "Starting http-kit webserver")
           (let [stop-fn (http-kit/run-server (var main-ring-handler)
                                              {:port default-port})]
               {:port    (:local-port (meta stop-fn))
                :stop-fn (fn [] (stop-fn :timeout 100))}))
  :stop (do (log/info "Stopping http-kit webserver")
            ((:stop-fn webserver))))

so i'll restart, get that error, but then restart again and things will be fine

(the error occurs during the stopping)