I grow one phal in semi-hydroponics in a very low humidity conditions under my HID lighting. It grows alot of new roots into the clay pellets. I notice every 7 days in the hot summers the reservior water level drops down to 5 mm before I fill it up to 5 cm.
I have a feeling that your roots may be too wet for too long a period of time in the orchidarium. Also the moisture level in the orchidarium is higher so it will not dry out very slowly. I think the colder temperature and wet condition in the winter and fall will cause root problems.