So this ability doesn't work like it should according to description. Is there any official comments about this? Is it bug in the ability, or mistake in the description?

How does it work then?

It’s working, on your next attack, not current swinging one. It’s a bit confusing but it does work. The killing blow doesn’t get free recovery but it’s the next attack u hit will not be affected by recovery.

So the description is wrong ( no 10 sec effect ), but the next action after you kill something has no recovery.

 

- That means a multi classed char can cast a spell without recovery after killing something?

 

- Does it matter how you kill it ( dots, spells, items like bombs or scrolls)?

 

And since we are talking about blood: does the speed bonus from bloodlust stack with itself ( when killing more than 1 enemy in 10 sec) and does it stack with frenzy?

I though that the buff that makes your next attack have no recovery lasts ten seconds. That is, for the next ten seconds, your next, ONE, attack is free of recovery. 10 secs of free no recovery would be too broken, and the free attack has to have some kinda time limit as well, hence the 10 seconds.