I have this same exact problem! I think it's the humidity and lack of. During the winter, we have the heat on, so it's much drier than during the summer. I had a beautiful rose I got for Valentine's day do that same exact thing. I kept it well watered, but the bottom leaves went dry & crumbly while the top leaves were pale like I was watering too much. I took it home & put it in my window with my African violets. It seems to be a bit happier there.. probably because it's much cooler in that window than at work.
