When you use a TNT or a Creeper to explode tall grass, like when you create an explosion in the Savanna biome, the Tall Grass drops itself, when it should just be obtained using some Silk Touch tool or in the Creative gamemode, but it didn't use to happen in the older versions of Minecraft. I don't know if this is a new functionality of explosions, but I think it's just a bug. However, it just happens when I use around 20 TNTs, with a big explosion... In the attachment you can see 2 Tall Grass drops, in the middle of the image.