Lifesaving Block not activating

This has happened to me several times, Lifesaving Block will not save me from a killing blow. Even taking facing into consideration, my cleric (Trogdor) cannot survive with this card. I will probably give up on shields with this card. What could I be missing?

 

Did the attack comes with a buff of any sort ? Lifesaving Block will not proc in such cases even with correct facing.

 

That has happened in the past, but not this time. Also, the battle log would have recorded that.