Observers don't trigger when a fence connects to a newly grown tree

The bug

A fence connecting to an adjacent block placed by a player or moved in by a piston causes the observer to trigger, a tree growing besides a fence does not, even though it connects.

To reproduce

1. Place a sapling

2. Place a fence next to it

3. Place an observer facing the fence

4. Place a redstone lamp or a piston behind the observer

5. Bonemeal the sapling
   → ❌ When the tree grows, the observer will not trigger the lamp / the piston

Video