Very interesting. So it seems to be that the aliens SHOULD spend the corresponding time units for priming a grenade but it seems not, right? And also quite many players seem to have experienced this problem. I myself also sometimes felt there's something strange about the aliens' throwing a grenade for some reason, but since they don't throw grenades that much frequently, I think I have neglected it so far. It would be great if there's a technical explanation for this problem.
Or is it just my misunderstanding? Honestly, I don't know
since I cannot remember exactly a single case when aliens had thrown a grenade and had yet enough time to do some other stuff: they usually just ran away IIRC. But also I doubt if it was just caused by mod conflictions...