If you place a plant in a flower pot (so far i think it works on anything that can go in a flower pot) when breaking the block below the flower pot (not the pot nor the plant just whatever the pot is on like for example a dirt block) after the block below is broken it will duplicate the item inside the flower pot. I've tried this under cobblestone, wooden planks, and dirt and they all seem to have the same effect when broken beneath the flower pot. As for more information this seems to be working on Minecraft 1.7.1 Pre-Release on the Server Version I have yet to test it on Singleplayer. Also for a side note I have also found that if you keep right clicking on a pot it will keep taking the plant and when breaking the flower pot you will only get back 1 of the plant and if you break the block below it, you get 2 back.

Hopefully this is indeed a bug and i'm not wasting anyone's time if this may have already been posted or is not a real bug at all and it's just some mess up on my part.

Thank you for your time!
~AmazingBlue