Toxin damage being inconsistent with non-bypassable shields

[calliph0re]

Spoiler

Apologies for the eye-cancer screenshot, but I think you can more or less tell what the issue is and it's not very easy to get a clean shot mid-combat (though admittedly I should probably darken my Sporelacer's energy colour a bit). As you can see, my secondary Sporelacer, modded for pure Toxin damage, is doing nothing whatsoever to the Sister's shields. I don't have other screenshots of this mission, but the direct impact of the grenade could damage her shields as normal, and the radial damage had no trouble once I took her shields down with my melee. I've encountered this same issue on Treasurers, and oddly enough on Minima Moa spawners deployed by Vapos Sniper Crewmen (haven't tested other Sniper Crewman variants but I'm guessing results would be similar), but not on any Sister's Hounds despite their shields also nullifying Toxin's bypassing effect - instead, their shields take the radial Toxin damage just like any other damage type, whereas the shields of Treasurers and Sisters are completely immune and prevent Toxin from doing anything until the shields are down.