Cactus Grows Next To Blocks

Cactus Grows Next To Blocks
What I expected to happen was...:
The cactus would grow and the second cacti would hit a block in the cactus farm, then it would be turned into an item and be sent down the water stream

What actually happened was...:
The second cactus grew next to the block and didn't turn into an item but instead stayed there

Steps to Reproduce:
1. Plant a cactus
2. Place a block vertically diagonal of it
3. Let cactus grow and touch block