What I expected to happen :
See the wheat uproot itself.
What happened :
How to reproduce :
Make a black room, till the dirt, plant a seed and update it (place a block aside, power it with redstone; change the light level (<9), etc).
Note about affected versions :
I guess the behavior of seeds changed in the first 1.7 snapshots.
Impact on the game :
Wheat don't need anymore light to stay planted.
Farm based on turning off light don't work anymore.
Sorry if I made mistakes, I'm not English