Stover bug: Immune to tranq, Attack until they fall over dead. (with no attack on my part, only Tranq)

[(PSN)YoshiandAmes]

Stover hunting in the Orb Vallis. 
Stover would appear, I'd tranq them, they'd attack for two minutes or so, never running off, just ramming into me over and over. (I'd be tranquing them repeatedly,moving around, emptying the tranq reloading, continuing to shoot) and then finally they'd fall over, like I tranqed them, but they were dead. They'd disappear a few seconds later.
I reloaded the map, tracked a few more stover (using the lure to get rare ones to see if it was just sentinels, it was not. All Stovers are seemingly bugged)
I tried using transference, having them chase me, Equipping and unequipping the tranq rifle, Using an ability to hold them down or in place and then tranqing them, Using different warframes, having different pets/companions. 
No set cave or spot, it was happening everywhere I encountered a stover.