Night was beginning on my hardcore survival world while exploring; I wanted to sleep through the night to prevent mobs from spawning, and so placed my bed at a nearby location to prepare for the night. (Which was under the shade of a tree, where a red mushroom was growing)
While testing this further on a creative world, also encountered this happening with double_plants
What I expected to happen was:
For the double_plant to be placed down, possibly 'popping' the mushroom if the nearby light level was too high, due to a block update.
What actually happened was:
The mushroom updated and 'popped' out of the ground; and 'broke' the double plant - 'causing the plant to drop as an item, but it left behind the "head" portion of the double plant.
Steps to Reproduce:
Create/find a dark room (e.g: through the fill command - "/fill ~5 ~3 ~5 ~-5 ~-1 ~-5 minecraft:dirt 0 hollow")
Grab a Mushroom (red or brown), a double_plant, and a light-generating block (Redstone Lamp, Sea Lantern, Jack o' Lantern, Glowstone, Lava... anything that creates a light level of 15)
Place the mushroom, place the light-block 2 blocks away from the mushroom, so that the light level on the mushroom is 13.
Cause the mushroom a block update by placing the double_plant next to the mushroom.
Observe:
The mushroom updates, sees that the light level is too high, so drops - expected.
The double_plant drops as an item, but leaves the "head" of a sunflower behind - unexpected.
The double-plant will only drop as an item if it is of a type that normally drops when broken, as opposed to only drops with shears. i.e: Rose Bush or sunflower, instead of double tall grass or a tall fern.
Placing the plant before the mushroom/crop does not 'pop' either item.
Additional Notes:
This occurs in both (+/-) X and Z directions
Used 'Night Vision' effect for the screenshots for visibility purposes.
Happens with crops when they have no light
Regardless of the type of double-plant placed (in creative or survival game mode) the remaining 'top' will be the sunflower.
The "head" of double plants does not appear to update upon placement/destruction of adjacent blocks; however, targeting the "head" and hitting the "use" key will update and remove it.
Water/Lava flowing next to the "head" of double plants will not update/remove them.
Unloading and then reloading the chunks will remove the leftover "head" of double plants
This can be done quickly by teleporting away, and then back, or by disconnecting from then reconnecting to the single-player world
Reloading the chunks through the "Reload chunks" debug option ("F3 + A") does not remove the leftover "head" of double_plants.
Placing the double plant adjacent to the mushroom (at y-1) where the "head" of the double plant updates the mushroom does not cause the mushroom to drop, nor does it affect the double_plant.
May also provide block updates to the mushroom through redstone dust updating up to two blocks away (+/- 2 away from the mushroom on the X or Z axis).
Duplicate of MC-49659, but MC-49659 should be a duplicate of this since this is more detailed.