Shadows Mana on Kill passive cluster doesn't work with traps half of the time.

It doesn't "work" in the way you're describing with any traps. Traps are not you - if the trap kills something, then it gains mana, not you.

Ah, yes. The trap's degens assign their kills to you since the trap isn't there anymore by the time they kill things, so they can't assign to it - as a result, degens from traps and similar owned entities have to be considered directly yours to prevent it being unable to assign the kill at all after the trap no longer exists.
This is non-ideal and we'd like to improve it, but for now that's how it has to go.