Everyone should understand that a "hold" means nothing. In fact the hold doesn't exist in the Senate rules. It is simply an understanding between Senators that once a "hold" is put on a bill, it doesn't move. It is part of the country-club, hail-fellow-well-met world of Senators, where I suppose principle matters less than than making sure all the ol' boys stay cordial.
As I understand it, "holds" have been defied before. Exactly why the Republican leadership failed to defy Senator Byrd's hold I don't know.
Because a Republican also had a hold on it, so it was mutually agreeable?