Crops that were growable in 14w20b pop out in 14w21b, unless the light level is the highest. The crops will pop out even when the light level is 12, more than sufficient for them to grow (if I understand the code correctly.)
I have searched for other tickets that fit this description, I found none, if there is one, I apologize for not seeing it.
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This is very different. Crops are of course supposed to pop out when the light level is too low, but at 8? or at 12? thats not how its supposed to work.

Please redo the screenshots with enabled debug screen (F3)

Confirmed for 14w21b:
Pop out when lightlevel is 7 or less (maybe intended)
*Added screenshots
Can you maybe make some screenshots too, while having the "F3"/Debug window open and standing on exact spot (that it shows the lightlevel)? 🙂

Confirmed for 14w21b:
Pop out when lightlevel is 7 or less (maybe intended)
This is intended, see the fix of MC-30877 and http://minecraft.gamepedia.com/Light
At a light level bellow 7, yes, they are intended to pop out. But this happened when the light level was 8 at the lowest.
Tested it in a different world, did not occur. I conclude that there is another cause to the phenomenon.

In fact there is an issue in 14w21b compared to 14w20b, see MC-56041
Works as intended. See MC-30877