[GAMEPLAY] Deathfire Touch not applying the correct DoT length?

It seems every spell is applying the 1 second DFT DoT regardless of the targeting type even though Rylai's appears to be treating all these spells correctly.

I was testing out Cassiopeia in a custom game to try and see whether each of her spells counted as Single Target, AoE, or DoT for things like Rylai's, DFT, etc. Her Q appeared to apply the 1 second DoT on every tick as I expected it to, as did her W which I thought might apply the 2 second DoT but could understand it going either way, but her E also applied the 1 second DoT with which I was somewhat surprised as it is clearly a single target spell. However, I knew that in the past her E was not treated as a single target spell due to its very low cooldown, so I figured it might be the case here.

But then I built a Rylai's and found E appeared to be applying the single target slow (1.5s duration 40% strength), so it seemed E was being treated as single target only for deathfire touch and not rylai's. I thought this might be a special exception but wanted to investigate further. Q and W were applying the weaker strength DoT slow.

Janna's Q and W both applied the same 1 second DFT DoT when they should clearly be applying 2 and 4 second DoTs, respectively. I did not test Rylai's on Janna.

Annie's Q and W both applied the same 1 second DFT DoT when they should be applying 4 and 2 seconds. Rylai's was proc'ing the single target slow on Q and AoE slow on W.

These were custom games in summoner's rift against beginner bots. DFT length was estimated by counting damage ticks, comparing to the length of rylai's slow, and mentally counting the time. Rylai's debuff type was determined by the effect on the enemy champion bot's change in movement speed and mentally counting the time.