this issue seems to be version agnostic, originally detailed in #69
however, 1.14 does not have purple sprouts yet

since potatoes and aubergine can be cooked, it would make sense that the sprout's loot tables would check for if the mobs are on-fire during death, and drop smelted versions of the food instead
in both 1.12 and 1.14 this check does not exist

Yes, that's definitely an oversight on my part.

This is fixed for 1.14. It needs to be adjusted for 1.12 still.