I experienced this when attempting to harvest cactus and wheat seeds from grass. Almost half the wheat seeds that were spawned while harvesting grass appeared to disappear as they hit the ground, and I was not able to pick these seeds up. This also happened when harvesting cactus, but I am not as confident of this bug, as the missing blocks may have all just landed on top of the remaining bottom portion of cactus (is this itself a bug? I don't know)
Comments 2
After re-examining the conditions in which this occured, I suspect it may have been because of the height at which I was harvesting. I was on a custom world, harvesting on the topmost block on which things can spawn. Maybe as the items fly up from the harvested grass, they could despawn as they cross the top of the block. I am not sure of the mechanics that could be at play at this height, but I have not noticed this since reporting it, although I am sure it was happening at the time.
Is this still a concern in the current Minecraft version 14w31a / Launcher version 1.5.1 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.