On Galaxy S4. Works in Creative and Survival.

Placing water or lava next to a cactus does not break the cactus. I expected doing so to break the cactus or, for lava, set it on fire.

Neither flint nor lava burns cactus. Placing lava on top of a cactus causes the lava to flow over the cactus without burning it. I'd expect the cactus to be gone (burned up) when I remove the lava. Instead, when I remove the lava, there's a cactus.

Cacti can also be grown starting under water and under lava so long as the other conditions for cacti growth are satisfied.

Finally, cacti do not burn when using flint to create fires next to them.