Missing quest givers? Cannot turn in a quest? Look here
 

Some quests require you to turn them in from the quest log. If you are using the Beta version of this addon from this website which works with this patch, this function currently does not work.

To fix this, press Alt-L to open up the Carbonite quest log. You can turn the quests in from there.

It does work in 4.030108, which shows a message in the Watch List and lets you left click the tracking button to do the turn in.

Alt-L is the Blizzard quest log, which does have a Complete Quest button as you said.

I really appreciate all your hardwork carbonite team, could you possibly make the area glow when you need to click the button. I actually had to start googling to figure this out because it's not obvious.

The text already alternates color from black to red. In yesterday's version I made the button a big yellow ?.