In node.js why does passport session stop formidable from triggering 'file' events?

In my app I am only using

app.use(express.json());
app.use(express.urlencoded());

and not

app.use(express.bodyParser());

so that I can manually parse file uploads. It seems that this line

app.use(passport.session());

stops formidable from triggering file events:

form.on('file', function(name, file) {
  //never called
});

How can I use passport session and not clash with formidable file event?