I've actually nailed it down a bit.
Appears the chest is nog gone. It is there, only not visible / accessable.
However, this is only true when my main char (who had the chest in his inventory) approaches the chest. If I leave him behind and approach the chest with my DK, it stays visible AND accessable! <img src="/ubbthreads/images/graemlins/silly.gif" alt="" />