I'm not sure what steps must be taken to recreate it, but flying around in creative on a world I had created in 1.8.1, I discovered a group of eleven cacti- spread out over a large area- that had been continuously "breaking" displaying destruction particles and subsequently dropping cactus blocks every 3-5 seconds.

Curiously, all cacti were found growing on hardened clay blocks, which may be the reason for continuous destruction, however of the 3 cacti in the immediate vicinity that were not displaying this glitch, 2 of them were also growing on hardened clay.