Wheat lacking light doesn't uproot if updated

What I expected to happen :
See the wheat uproot itself.

What happened :
It didn't.

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}