modifying a block around a cactus destroys
Linked issues
is duplicated by 6
MC-8795
Desert-When placing sand by a cactus, the cactus breaks.
Resolved
MC-16843
Hay Bale breaks Cacti when placed
Resolved
MC-25863
Cactus is destroyed when a block is placed beside it
Resolved
MC-36032
Cactus block is being destroyed when another block touches it
Resolved
MC-62085
when I use a sign on a cactus it disappear
Resolved
1 more links
From the Minecraft Wiki: When the spot a cactus is placed in becomes unsuitable, such as when a block is placed next to them or their own sand block underneath is harvested or falls, the cactus block and any above it collapse into blocks that can be collected and placed again.