Masdevallia trouble?

[greenpassion]

I have 2 masdies that I grow in S/H. They've been in this for several months now, although I purchased them in the usual potting medium, from a reputable nursery. They are under lighting with my other orchids, phals and oncidiums, on a heat mat with a fan for circulation, and a humidifier. All my other orchids are doing great. New root growth, spikes, etc. But my masdies are a puzzle. :_One is continously losing leaves, although it also constantly sends up new growth. The other is just there. No new growth, but it looks nice and green, never losing a leaf, but never growing any either. As I said, the light is good enough to make all the other plants really happy-but what is going on with my masdies?