Looks like it will continue broken until Turbine finally decide to fix those Gelatinous Cube / so called "changed status monster/object".
Make an already unpopular quest even more unpopular -- glad I test it myself so I won't make a whole party disappointed again.
(For whoever didn't know, this quest broken since the very first so called "AI fix")
Oh and, yes, I have bug report it in the first time and the GM also told me do so (after I submit the ticket, waiting 20 mins then give up, done another quest then he fially show up)