I just hard locked when throwing an incendiary on top of a hephastis, related?
Was in a bush, badly beaten, ejected just ahead of destruction. C8 on an uller, it died, turned around and tossed incendiary on top of the hep, instant hard lock.
EDIT: Repro on my own hep with incendiary. Also on the Huit. Seems all turreted vehicles are locking you if you land a grenade on them.