If you reorder a bitstream from first or last position to an intermediate position it should get both its up and down arrows enabled, but doesn't. If you view the html source before reordering you will see that the first and last rows have:-
class="... disabled disabled ..."
After reordering only one of the 'disabled's is removed. There obviously shouldn't be two in the first place. Not sure where the problem lies but probably in the XSL generating the page.