When cactus grows with another block on side cant break cactus

What I expected to happen was...:
I came to check 2 of my cactus farms i checked too see if its fine

What actually happened was...:
So when i looked at the top i realized that the cactus is right beside the glass which it suppose to break the cactus which it let it grow and i had to destory it manually

Steps to Reproduce:
1. Put cactus on sand.
2. Then put a block on were beside were the second stage growth .
3. Then you should see later the cactus is right beside the block.