I have one that's much larger (Den. Antler Hybrid Purple), and I'm having a similar problem. My leaves are turning yellow, shriveling, and falling off. Not all of them of course.
King_of_orchid_growing - When you say be careful of temperatures, what do you mean? I'm growing it in my house, but suspect that the AC may be the problem. I live in Houston, so summer can be pretty brutal. However, if they like it hot, then I can certainly provide that.