If its not happening to all your plants then that plant or plants are in a hot spot get more air flow over the tops of your plants. Your room can be 90 consistantly and if you have great air exchange and circulation your plants will be fine. I may be wrong but I think plants grow faster than when they were in 85-90 degree temps consistantly with good air flow, than in constant 75-80. I know that goes totally against the grain and textbook but its just my experience.
Edit: Im not talking about adding Co2 either just natural fresh air.