Occasionally this "Glitch" occurs after playing Broken Sword 5: The Serpents Curse Episode 1 and you are still prompted to purchase episode 2.
Following the purchase of Episode 2, and when choosing to "continue with Episode 2", you are immediately taken to the credits or to an auto-save with George and Nico in the cave with Gehnen. This is the end of Episode 2. Not Episode 1. Episode 1 ends with George and Nico escaping Hobb's burning studio in London.
This does not mean you have missed out on Episode 2. What has happened is that the game has automatically proceeded on to Episode 2 without prompting you for purchase.