This is a bug that has been reported on earlier versions of MC but it still affects snapshot version 15w31a, though it may have been partially corrected from earlier versions. When you hit the bottom half of a double-high plant such as Double Tallgrass, Large Fern, Rose Bush, or Lilac, the top half briefly turns into a Peony flower. I believe it used to be (though I could be mistaken about this) that no matter where you hit them, the upper part would turn into a Peony. Please completely fix this bug. This bug has gone unfixed for the last several versions of Minecraft (possibly back as far as 1.7.x or 1.6.x). And a partial fix (which may exist in this latest snapshot) doesn't count. No matter where I hit the plant to destroy it, no part of it should briefly turn into a different plant.