Affects Version/s: Minecraft 1.8.8, Minecraft 15w46a, Minecraft 15w47a, Minecraft 15w47c, Minecraft 15w49a, Minecraft 15w49b, Minecraft 1.8.9, Minecraft 15w50a, Minecraft 15w51b, Minecraft 16w06a, Minecraft 1.9 Pre-Release 1, Minecraft 1.10.2, Minecraft 16w41a, Minecraft 16w42a, Minecraft 16w43a, Minecraft 1.11, Minecraft 1.11.2, Minecraft 17w14a, Minecraft 17w16b, Minecraft 1.12.1, Minecraft 1.12.2, Minecraft 17w48a, Minecraft 17w50a, Minecraft 18w07c, Minecraft 18w20c, Minecraft 1.13-pre3, Minecraft 1.13.1
Fix Version/s: None
If you place a carpet,
banner or sign on the top block of tall grass or large fern, it replaces the top block and uses the lower block as a support block. Shortly after, the lower block disappears, making the the carpet, banner or sign break.
17w48a: Banners and signs no longer affected. (Maybe because
MC-86980 was fixed)
Based on 1.11.2 decompiled using MCP 9.35 rc1
Signs and banners are not properly overriding the method net.minecraft.block.Block.canPlaceBlockAt(World, BlockPos), instead they test if they can be placed in the method net.minecraft.item.Item.onItemUse(EntityPlayer, World, BlockPos, EnumHand, EnumFacing, float, float, float). This method allows the item to be placed facing up (= on the ground) without checking if the block below is solid if the block it is placed on is replaceable, which causes problems with double plants.
Carpets appear to override the method canPlaceBlockAt "correctly" by testing if the block below is not air. The problem is that once the upper part of the double plant was replaced the lower part is air and therefor the carpet drops.
When banners were affected (before 17w48a), another bug was discovered by reproducing MC-92758. When a non-black banner replaced a top block of tall grass or a large fern, a black banner drops, not the color of the banner placed. A bug report containing this seems to not be created yet.