Minecraft wiki entry for Block_update, associated text: Exception
Some changes do not produce General NC updates:
Bamboo
Thickens when the upper bamboo thickens.
Bamboo shoot
Grows into a bamboo.
Water and Bubble column
Converts to each other.
Carved pumpkin, Jack o'lantern, Snow block and Iron block
Turns into a golem.
Plants
Turns into a double-block plant.
Cauldron
Its water level changes.
Chorus flower and Chorus plant
Grows, ripens or changes its shape.
Cocoa
Grows.
Redstone repeater
Be lit or unlit.
Redstone comparator
Its signal or its mode is changed.
Coral, Coral fans, and Coral blocks
Dies.
Wheat, Potatoes, Carrots, and Beetroots
Grows.
Doors, Trapdoors, and Fence gates
Opens, closes, actives, or deactives.
Dragon egg
Transports to destination.
Farmland
Gets hydrated or dry.
Frosted ice
Melts gradually (but has not turned into water).
Jukebox
Inserts or ejects records.
Nether wart
Grows.
Observer
Be lit or unlit.
Redstone lamp
Be lit or unlit.
Sea pickle
Increase its number using bone meals.
Sponge
Absorbs water.
Melon stem and Pumpkin stem
Grows
Remove the melon or pumpkin from it.
Sweet berry bush
Grows
Its fruits are collected.
Turtle egg
Its number decreases.
Vine
Grows, changes its shape, grow out a new vine block.
Wither skeleton skull, Soul soil, and Soul sand
Turns into a wither.
Grass block
Be eaten by a sheep.
Carrots
Be eaten by a rabbit.
Anvil
Damaged.
End portal frame
The Eye of Ender is placed.
End portal
Generates.
Brewing stand
Bottles or potions are added into it.
Structure block and Command block
Changes its mode.
Cactus and Sugar cane
Grows.
Daylight detectors
Change its mode.
Dispenser, Dropper, and Hopper
Be activated or inactivated
Fire
Its age or shape changes.
Saplings
Increases its stage.
Tripwire
Its "disarmed" value changes.
Beds
Be occupied or unoccupied.
Nether portal and Obsidian
Generates as a nether portal.
Nether portal
A nether portal be activated.
Campfire
Add or remove hay bale below it.
Fences, Stairs, Glass panes, Iron bars, Mushroom blocks, and Walls
Its shape changes.
Grass block, Podzol, and Mycelium
Be covered or uncovered by snow.
Kelp, Weeping vines, and Twisting vines
Grows.
Add or remove kelp/vines above/below it.
Pressure plates
Its signal changes.
All blocks
Change its blockstate using debug stick.
Placed by a command.
Pistons, and Beds
Have more complex behavior.