On our development server one of the players has noticed that something rather strange seems to happen when you are breaking a 2x1 stack of seeds. I believe this to be a vanilla issue as we can see no reason for it to otherwise be happening.
The video of it happening is: https://www.youtube.com/watch?v=cPqthX0pLYo&feature=youtu.be
This is running on the latest Spigot build and using the 1.8.1 client to test. We have managed to replicate it with multiple people and believe it to be a vanilla MC issue.
If you need any more info I will try to provide it as you need it.