wont remove cacti when block is above and to the side

the cacti growth problem

What I expected to happen was...:
My cacti farm should have had the cacti remove because of a block above
he cacti.
What actually happened was...:
The cacti grew by the block

Steps to Reproduce:
1. Have a sand block with cacti
2. Place four blocks in T without left spot
3. Remove all blocks except the far right