I just recently, by bad luck ended up torching one of my paphs- i was thinking infront of the east window- no problem, wrong! One side of the fan has the deep brown/black marks and the leaves are soft at the base and are crunching up and will fall soon. I think I might have lost my spike this year as well :S ...
If it sounds like my situation then you probably have burn, but if all your paphs are facing the same light source and thats the only one-- could it possibly be closer or in the direct path of light?
Anyhow, hopefully it'll be back up and healthy in no time