Abyss omens don't work when desecrating armour?

I have a rare helmet with 2 preffixes and 2 suffixes, I want to desecrate it and get specific modifier from Kurlag group of modifiers, so I use Omen of the Blackblooded to target Kurlag modifiers, but when I have the omen active in my inventory and I try to use Preserved Rib on the helmet - nothing happens, except a message in chat saying "Omen is incompatible with this Desecrating item".
Is this a bug?