How do I get "10 vulnerable machine kills"?

While the trophy description seems extremely straightforward, I think there is more to it than it sounds. The description is simply:

Killed 10 Machines weak to Fire while burning, or weak to Freeze while frozen.

However, I've taken out 6-7 Corrupted Zones by setting all Machines within them on fire and made sure to let them die while burning. At this point, I'd estimate that I've killed at least 20-30 Machines weak to Fire while they were burning, yet this trophy hasn't popped. Do I need to kill them with non-elemental damage while they're burning/frozen to get the trophy or something?

Solution 1:

I got the trophy after killing 10 Corrupted machines with burning damage such that the +100 Burning Kill text appeared on screen. (I was not myself on fire at the time.)

Because I originally assumed the exact opposite based on the text of the trophy -- that the machine would have to be on fire and then I would have to kill it by some other means -- I was quite surprised when the trophy popped.

Solution 2:

I think the game may have a flaw where corrupted machines do not count as "vulnerable to fire" machines for the purposes of quests and trophies. I tried to finish a tutorial "vulnerable to fire" quest and none of the corrupted machines seemed to count. I switched to an uncorrupted machine marked as fire vulnerable and it worked fine.