Sometimes when I go harvest nether wart the nether wart becomes like bedrock and cannot be broken except by destroying the soul sand it is on. It appears that when I quit to title on go back in to the game several times or go too far from the nether wart it becomes indestructible.

What usually happens/is expected: Nether wart breaks.
What sometimes happens: nether wart becomes unbreakable.
How to reproduce:
1. Plant some nether wart on soul sand
2. Go onto survival
3. Try to break the nether wart
4. If it breaks quit and go back in several times and wander off pretty far then go back
5. Attempt to break it (Note: this occurs 10-20% of the time to me)