edit: OMG, am I idiot or what. Nothing to see here, move along please. My mistake. But just for other to see my error I will leave it here.
"manslayer" does not proc elemental effect you have, those numbers are on crit effect=shocking burst+icy burst, they are just in two lines instead of one as I'm used to.
Was testing manslayer effect with handwraps and I don't thing it should work as it does when attacking non humanoids.
When manslayer proc on non-humanoid using weapon, it will pop "immune" text in floating dmg numbers, but if it proc with handwraps, then it appears it will proc all elemental effects you have.
here is how it looks with wepaon:
and here with handwraps:
I have no source of doublestrike and it happens every time.