I've completed Season 1 and completed 400 Days last night. When I decided to replay it today I found that the game thinks I'm back to not having finished episode 5; I get 'play' options for both EP5 and 400 days, not 'replay'.
When I look in the Telltale folder on my PC I can clearly see a file called 'save_75.save' which was created yesterday when I played 400 Days.
What's going on? If I click play on 400 Days it asks if I want to randomise my play data!