I also have a problem with this.
Pressing alt-L does not show me the default questui so cannot turn in that way.
Cannot press red text with questionmark, but it is there.
And i get no lua-errors even with lua-errors enabled.
Had to disable Carbonite to turn it in. The quest was this one:
http://www.wowhead.com/quest=26144/prisoners .
Carbonite v.4.22
Edit: Writing this as i am questing , in a follow up to the previous quest, it works. Namely this one:
http://www.wowhead.com/quest=26154
There i get the Yellow Questionmark that i can press to turn in quest.