Minecraft 14w21a, Minecraft 14w21b, Minecraft 14w26c
Java HotSpot(TM) 64-Bit Server VM, version 1.7.0_55, running on Windows 7:amd64:6.1
Wheat sprouts revert to seed under the following conditions:
- adjacent to planted blocks at light level 15 (which in turn must be less than 4 blocks from a water block)
- seeded blocks at light level 14 or lower, for example in the shade of a tree (seeded blocks must be less than 4 blocks from a water block)
- Wait until nightfall (time set night)
- Approach seeded blocks and the seeds will jump out.
This does NOT occur at 14w20b!
Picture shows jumping seeds from blocks at daylight level 14 (standing on 13).