Normally, when you chat and press the up arrow, it auto-fills your previous message. However, when you are in a bed, if you type something in chat and then try to press the up arrow, it will go to your most recent message when you were not in the bed. Example: 

<Player> Hello

**gets in bed**

<Player> How are you?

If the player then presses the up arrow while still in bed, the chat will auto-fill to say, "Hello" instead of, "How are you?"