People who flip the script on you are nothing but people who have not even read the script. They do not even know how the story begins or ends. They see you have either read the script, or are further along than they are, and they want to see what it is you know. So they turn it over. They turn the pages around so they can read it and you cannot. They want to read it to you. Let you hear it from their mouth, instead of you reading it on your own. That is how they fool you. That is how they truly flip the script. You have to reread the script yourself after they have messed it all up, and added things that are not in there from the beginning. That is what flipping the script means.
Do not let anyone take the script from you. Have an extra copy for yourself if you have to. Read the entire script from beginning to end. Do not skip a word. Read it more than once if you did not comprehend it the first time. If you do not have an original copy, then get you one. Keep one around for reference. Be able to recite important lines from the script for yourself. Interpret the script to understand it the way it was intended to be understood. Never flip the script.