Given the number of theories so far, I’m surprised no one has suggested this one: Aftermath 2 is in fact meant to demonstrate that Snape’s behavior has not changed, by displaying behavior that is entirely typical and expected of him; but now that Harry, Minerva, Dumbledore and the readers are all primed to look for changes, they will find them even where they shouldn’t.
Given the number of theories so far, I’m surprised no one has suggested this one: Aftermath 2 is in fact meant to demonstrate that Snape’s behavior has not changed, by displaying behavior that is entirely typical and expected of him; but now that Harry, Minerva, Dumbledore and the readers are all primed to look for changes, they will find them even where they shouldn’t.