When I destroy a tall plant (Double Tallgrass, Rose Bush, etc), it seems to place a sunflower & remove it after a second. I created another world & tested it again just to double check, it still happened.
After nearly 100 times of pressing F2, I eventually got a picture of it.

Edit: It also happened in 14w19a, but it came up with "No Matches" when I tried to add it to "Affects Version/s"