When I tried creating a tree farm made by the YouTube user Mumbo Jumbo, the sand blocks breaks instantly when trying to push them using pistons. This worked in 1.5.2. People in the comment section seem to have problems with this as well. See attachents for a video on it.
The clip can be found here: /watch?v=qEOB1zrNaVM
Duplicate of MC-6438, the title of which should really should be updated.