Return of Reckoning

With tactic Frenzied Mayham every finishing move when used burns all thorns and gets the benefit of extra 15% critical chance. This is for every instant finishing move but when it comes to Ruthless Assault I have observed that thorns are gone once I start channeling Ruthless Assault (the very first moment I cast it).

I would like to ask if the bouns stays for the full channel cast time or is gone after first hit (out of 6 hits) of this ability.

Thank you!

Gone after first hit...ive been testing for a few hours.. RUthless assault not worth using since dont apply auto atacs.