Every other block in the game which spits out some form of item (jukebox, item frame, berry bush, lectern etc) always drops the item on the ground, and does *not* add the item to the player's inventory directly.
Flower pots break from this standard by directly inserting items into the player's inventory when right-clicking to remove the flower. This is inconsistent with every other instance of such usage.
This is working as intended, see MC-169496