It's not, as this a clientside/serverside bug that vanilla environments don't have access to reproducing. However, I'm very confident does exist even in vanilla environments.
Updated the description.
I was there with CmdrGod when he encountered that bug (You can see me in chat). We had this issue when we were replacing one of Minecraft's biomes with our own, the nether_wastes biome. We used some in-game Plugins to change the biomes of the terrain you see. Most of the terrain it covered pretty solid, however some it didn't. Even when we F3'd the biome of the terrain that was bugged, it said that it was nether_wastes.
Addendum: Upon further testing, escape sequences such as \r and \b also don’t work for /tellraw in this version.