I have noticed many threads on this subject going back quite a few pages, so it seems it is a BIG bug.
The jist of it - You cannot plant seeds on corpses.
- Ive tried the 'official' work around..change E key bind, abandon quest, etc etc and nothing..
- The unofficial work-arounds where you wait for a soldier character to respawn and then try planting seed on previous killed corpse no longer works as it seems the corpse disappears just before the character respawns making that technique impossible.
frankly these are all techniques that should never be possible if the quest worked correctly.
What makes me laugh is i completed this quest right back near the launch of the game where there was a different bug near the end that was fixed quite fast.