Cactis are not poping off

Put the summary of the bug you're having here

*What I expected to happen was that the cactis poping off so i could collect

*What actually happened was that the cacti grown up even if the was a block besides it !!

Steps to Reproduce:
1. Put 1 block of cacti on the sand
2. Put a block besides it but 1block higher than the cacti
3. Wait and the cacti will grow but it will not pop off