If you are using the "Enhancement Disabled" style, forum description bubble (and a lot of other bells and whistles) does not come up. However, if you hover your mouse over a thread title, the style still makes that extra ajax call and brings up animation with the thread preview.
I'm not sure if this is intended by the style, or if it is a slight oversight in the process of disabling animations. If it is the former, and we can configure whether or not thread previews appears via a style property, then we can safely ignore this. If it is the latter, then I think it is a bug that would need to be fixed.