I think we need a more prominent hint either way, and even more so if we change existing behavior. The lack of that hint is the bigger problem; what behavior we assign to up/down is the smaller one.

(Also, we are not talking about normal scrolling behavior either way, are we? We are animating the panel on up/down, and we are talking about keeping that animation, but reversing the directions. Not animating at all would certainly be more consistent with the wider web, but also somewhat inconvenient IMO, as there is little practical use in opening the panel partially, and standard up/down key behavior is slow. I agree with Fabrice here: if we want to change directions, we should reconsider the whole metaphor. E.g. the chevron initially pointing up and then changing direction doesn't really make sense in a scrolling model.)