A lot of the blocks that use flat planes in their geometry have messed up shading when deferred rendering is enabled. Instead of the light reaching all planes evenly, one plane is lit on both sides while the others are completely dark.

List of affected blocks (may be incomplete):

• All small flowers;
• All potted plants;
• All saplings (not counting the propagule);
• All corals (including dead variants);
• All coral fans (including dead variants);
• Sea pickle (only the bright part);
• Sugar cane;
• Dead bush;
• Bamboo (sapling and leaves);
• Grass;
• Fern;
• Seagrass;
• Kelp;
• Wheat, beetroot, potato, carrot, torchflower crops;
• Both dripleaf types;
• All double plants except for the pitcher pod;
• Both mushroom types;
• Both fungus types;
• Both Nether vines;
• Both Nether roots;
• Nether sprouts;
• Nether wart;
• Glow Lichen;
• Spore blossom;
• Hanging roots;
• Cobweb;
• All amethyst sizes;
• Chain;
• All hanging signs that are attached to a rod by two chains.

Some of the recent additions to the game that use a different cross model without mirrored textures are unaffected by this issue:

• Pointed Dripstone;
• Cave Vines;
• Pitcher Plant;
• Pitcher Pod.

Additionally, the mangrove propagule and the pink petals are in a weird middle spot. They just don't have any shading at all, so while they don't look out of place I can't tell if it's intentional.