Bukkit

What steps will reproduce the problem?
1. Place sponge near Cactus
2. Destroy sponge near Cactus
3. Profit. (Cactus gets destroyed)

No big deal, just thought you might want to know this. :)
Love your plugin!

Eh... With the method used to fire off the physics events, there's not really a way I can fix it efficiently.

A block 36 is placed on each air spot that is no longer sponge-protected. Apparently, block 36 can destroy cacti (despite it being an almost invisible block) :/

I suppose I could try catching the block physics event for cacti and cancelling if it's caused by block 36. I'd have to make this optional though, so that server with huge cacti farms aren't lagged.

We'll have to see how it turns out after experimentation. Thanks for pointing this out!