Observer not updating when tree grows leaves in front of it

The Bug

I've got a pretty bog-standard tree farm where an observer detects tree growth, but that has since broken in this snapshot. It was working in all previous snapshots. When the tree grows the observer does not give off any redstone signal, but when I break the leaf block that appeared in front of the observer, it gives off a redstone signal and the pistons fire off like normal. This is on a single player world.

How to reproduce

1. Setup an observer to detect a leaf block of a growing tree
2. Grow a tree
   → The observer does not trigger.

Note that observers still detect log blocks.