Total mess with already generated worlds,Entire Swamplad is affected.
That on the screenshot was Witch hut and surrounded with wood
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Invalid.
If you are updating from 14w26a or 14w26b, your saved world has corrupted blocks and it will be heavily damaged once you open it in 14w26c. Please use a world backup that was saved with a pre-14w26 version.
Never use snapshots without first making backups of your saved worlds.
Source; https://mojang.com/
Did you update from 14w26a or b?