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:

1. Create/find a dark room (e.g: through the fill command - "/fill ~5 ~3 ~5 ~-5 ~-1 ~-5 minecraft:dirt 0 hollow")
2. 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)
3. Place the mushroom, place the light-block 2 blocks away from the mushroom, so that the light level on the mushroom is 13.
4. Cause the mushroom a block update by placing the double_plant next to the mushroom.
5. 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).