When you type "/help a" in the Chatbar the chatbar reset to "a". When you type in any other letter it doesn't reset.
Edit by [Mojang] Mega_Spud (Jay Wells):
- Start the game in 126.96.36.199 Retail and open a world
- Open the chat bar
- Press CTRL+Esc (focus moves from Minecraft)
- Click focus back on Minecraft
- Type some text or a command in the chat bar or inventory search