Observer Does Not detect Nether Wart Growth

Steps to Reproduce:
Place an observer with the detection side facing the nether wart.
Optional: Place a lamp/bulb on the output side to easily tell when it fires

Or download the structure attached and import it into the world, then press the button next to the water (note: sets random tick speed 1000 on the last chained command block)

Exspected Results:
The observer fires when the nether wart grows.

Observed Results:
The observer does not fire when the nether wart grows. Other crops do which it it is odd.