Minecraft wiki entry for Development_versions, associated text: Pistons no longer get into a state where they pause, activate randomly, and potentially crash the game
Sticky pistons and slime blocks can no longer pull and break comparators
Shulker boxes will no longer be dispensed as items if the dispenser is obstructed
Burned out redstone torches will no longer reactivate until they receive a block update or are replaced
Redstone now correctly powers adjacent blocks
Observers no longer visually cut redstone dust
Rails will now take block power into account when attaching to other rails
Dispensers, droppers, and redstone lamps will now activate properly when redstone dust is placed on top of them
Automated chicken cookers using slabs will now function properly
Trapped chests with slabs or stairs above no longer powers redstone dust adjacent to the block below it when the chest is open
Glazed terracotta can no longer be pushed using slime blocks and sticky pistons
Minecarts no longer get stuck when passing through blocks on diagonal rails
Armor can now be equipped on an armor stand using a dispenser