In the movie, it was very clearly implied that Hermione and Ron told Maggie Smith about what had happened.
All of the rest you mentioned are just examples of why I cannot fathom how a series of such poorly plotted, acted, et cetera, movies could garner a fan base. The very idea that a gang of wizardly children would even submit to mass torture itself is ludicrous. They're ready to fight the Forces of Darkness, but can't stand up to a single bully? The parents of students who themselves are wizards couldn't do anything except withdraw their children? Absurd. That any institution could torture students with impunity and still retain any semblance of prestige is likewise ludicrous. It is quite obvious that important members of the faculty knew what was going on in the movie. That they chose to protect their jobs rather than their students reduces them to the status of moral cowards at best.
I watch a lot of movies, and OotP is easily one of worst I've seen this year.