This bug happens around coordinates -468, 64, 194 in a Superflat world with seed -7993066103807340761 using the following preset:
3;1*minecraft:bedrock,59*minecraft:stone,2*minecraft:dirt,1*minecraft:grass;1;village,mineshaft(chance=0.01),stronghold(chance=32 count=3 spread=3),biome_1(distance=32),dungeon,decoration,lake,lava_lake
When I visit a village, flowers and seeds show up as loose items on the gravel roads. This is probably caused by their having generated (on grass) before the village roads were generated, and then uprooting when the grass blocks are replaced with gravel (I've been able to reproduce this behaviour with a /setblock command block). If the villages generated before the flora, or if the roads were generated with air spaces above them (which would have the extra advantage of adding tunnels in hills where needed), it'd look more like they'd been built long enough ago for any litter to have despawned (or by someone who'd cleaned up after themselves).
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kumasasa
Duplicate of MC-610
If I rewrite the preset to put "decoration" before "village" in the comma-separated list after the last semicolon, then some grass blocks spawn on gravel (a normally impossible state), and disappear if I place a redstone lamp (even with no inputs) or torch nearby. This reinforces my belief that the bug lies with the order in which things generate.
3;1*minecraft:bedrock,59*minecraft:stone,2*minecraft:dirt,1*minecraft:grass;1;decoration,village,mineshaft(chance=0.01),stronghold(chance=32 count=3 spread=3),biome_1(distance=32),dungeon,lake,lava_lake