I still think environmental factors come into play - they (or rather she) just doesn't like/feel comfortable in the enclosure. I have heard they don't like the wind for a start.
I agree, I think environmental factors for keeping giant pandas are crucial, in addition I think the lack of a wide variety of bamboo may also be relevant.
Out of interest, does anyone know if the contract with the Chinese means that the current pairing cannot be changed in any way ? Ie; to exchange one animal of the present pairing ? Or does the pair have to remain together for the duration, despite possible incompatibility issues ?