Witch hexblast skill problem?

Hello Guys,

Have a question/issue about hexblast mechanics:

I made a build where a core DPS is hexblast + Whispers of Doom passive (You can apply 2 curses at once) + Blasphemy (curses apply by constant aura).

I also added 'spell echo' skill to hexblast ("supported spells echo once") so it should echo once again. Meanwhile nothing happens and I am wondering why? Is it a bug or I don't understand/know mechanics? My thinking here is that even if curse need time to apply, hexblast description says it 'detonates a curse' not curses so using whispers of doom shoud apply? Still nothing.

Cheers