Can't type with Keyboard on Signs

Sometimes, when I try to place a sign or put it on a wall or edit it, it won't let me type in it. I've tried restarting the game, and it worked again at first. Then I tried editing another sign and the problem happened again. It happens in Singleplayer and Multiplayer. My friend connecting to my World has the same issue too.

Steps to reproduce:

1. Load a world.

2. Place or edit a sign. It usually lets you type at first.

3. After you try to place or edit more signs, notice how it sometimes doesn't let you type anything on the sign.