no leaf decay

Put the summary of the bug you're having here

What I expected to happen was...:
I expected leaf decay with sappling drops and the occasional apple

What actually happened was...:
there was no leaf decay after 30 minutes of waiting

Steps to Reproduce:

1. download and install 18w47a
2. create new survival world 
3. punch a tree into submission, removing all logs until only the cluster of leaf blocks  remain

4. observe the wondrous absence of decay