Whispers of doom only works when 2nd curse is cast with 1st weapon regardless of allocation

I have whispers of doom allocated with a general skill point, not a weapon set. yet it only works if i cast the 2nd curse using my 1st weapons set. I have blasphemy running with Temp chains but when i cast despair with my 2nd weapon set. It does not take effect, and will only take effect if i cast it with my 1st weapon set.

I confirm this is also happening for me. It drove me nuts because it was happening randomly. In one zone I could use the second weapon set to cast the curse, whereas in another zone the curse would not apply!!! Plus, please be careful at the level of your curse gem. I had temp chains not apply because it was level 17. The gem description would say "Curse does not apply to enemies over level 78" and after I leveled it to 18 it now works fine and the text in the description is gone.

It's a shame curses don't work properly on different weapon sets