Yet another cool feature would be to have the recommended action field change colour as per the recommended action - green if a sell, red if a buy and some neutral color for hold. Gives a psychological reinforcement to the pending action. Just a thought..
I just tried what you describe and I see something a bit different. I can update the first portfolio to Sept. 17th. It appears to work fine. However updating subsequent portfolios is as you described. Definitely a bug I'll have to fix.
I'm surprised nobody else has reported this before, perhaps nobody updates manually and backdates at the same time.