Losing session data with Rack::Session::Pool

[auxbuss]

This gist https://gist.github.com/3899237 demonstrates a problem I discovered while testing. It can be run as a standalone test.

When making consecutive calls to a sinatra app, the whole of the session is empty on the second call when the first call uses flash.

I've left in a debug in sinatra's before to show that the expected session data is not there on the latter call.