Resolution: Works As Intended
TLDR: Ferns are scientifically plants that do not have seeds. 1.15 fixed a "bug" that made tall ferns not drop seeds. This should have, even if unintentional, been left and small ferns should have been moved over. Not the utmost priority bug, I assume, but a nitpick from a fan.
Ferns have the following scientific classification.
Under the Tracheophyta, they are a member of the subclade Euphyllophyta, which means they are vascular plants. What is interesting is that they are not classified under Spermatophytea, as flowers and trees are, but instead as Polypodiopsia. This class is relatively unique in that plants here are vascular but do not have seeds.
The above table is what was formatted when I snagged it from Wikipedia.