No problem, its usually when you go into combat, your player opens the curtain stands out then closes curtain, runs to stairs then runs back to curtain. Usually at this point the Menaphite thug is standing directly right next to the curtain, when you open to go back in the npc walks out and you go in and then close the curtain and then nothing happens. It happens most of the time if the npc is by the curtain, if hes on the other side then your most likely okay.