It is because you are using the dataTags incorrectly, you have to do it like this: /summon Item ~ ~ ~ {Item:{id:1,Damage:2,Count:1,tag:{CanPlaceOn:["redstone_block"]}},PickupDelay:0}
This bug tracker is only for the PC edition of the game.
I have it too, it seems like all 2-block tall flowers have this problem.
confirmed, I have it too.
Reply to Jeff Isom:
Actually it was not, my brother and I tested it in 14w25b.
I get this very much too, even on singleplayer. I made a whole minigame for 1.8 and now I can't release it because of all the lag.