When you right click a flower pot that has a dandelion, poppy, cactus, oak sapling, mushroom or dead bush inside, while holding something that can be placed in a flower pot, the plant you're holding will replace the one in the flower pot.
Steps to reproduce:
1. Place a flower pot with a dandelion (or any of the plants above) in it.
2.Right-click it while holding a poppy (or another plant).
3.The poppy replaces the dandelion in the flower pot and the dandelion is lost.
Confirmed.