I just did a mistake using the //replacenear command
Instead of replacing all the wood with air on a radius of 64, I replaced all the air with doors on a radius of 17
The falling doors caused a deadly lag on the server... so I think it would be a good idea to do a check to make sure such a thing cannot happen.

Something similar also happened when someone replaced smooth stone on which minecart tracks were placed with glass. It caused a track rain which pretty much made the server unusable.

Oh, that's a good suggestion. I once accidentally spawned tens of thousands of torches which didn't go down well with the server.

Moved: http://redmine.sk89q.com/issues/75

I remember doing this with flowers (back long ago when WE didn't use item names and didn't have a block whitelist).

I apparently forgot to put in an item blacklist when I converted the block whitelist setting to a blacklist setting a few weeks ago. I'll fix that.