I know that this bug has been a long standing one, but as far as I know, the last time it occurred (1.7.5), it was 'fixed'. However, it seems to have happened again.

Basically, whenever I break a block, it reappears and then after about 5 seconds, disappears and drops the item entity.

The unusual thing is that this hasn't happened before really in 14w28b. So, it could be a factor of things. But after a few tests, it seems to be Superflats causing the problem

And a quick update.. I increased the amount of layers (by increasing the amount of dirt in the Superflat Preset), and the problem no longer occurs. So, I don't think it's down to FPS issues as the more blocks the world has to load, the more power it should take.. (I'm not sure on that bit, but I think that's how it works)