JSON signs with scoreboard values go blank after relogging.

In single player, signs that have scoreboard values printed on them will go blank after relogging.

You can recreate the issue as follows:

1. Create a new, super flat world in creative mode, in peaceful difficulty, with cheats turned on.
2. In chat, run the following command: /scoreboard objectives add myObjective dummy
3. In chat, run the following command: /scoreboard players set myPlayer myObjective 9001
4. Give yourself a sign, a command block, and a button.
5. Place the command block down in front of you.
6. In the command block, write the following command: /blockdata ~ ~1 ~ {Text2:"{\"score\":{\"name\":\"myPlayer\",\"objective\":\"myObjective\"}}"}
7. Place the sign on TOP of the command block.
8. Place the button on the side of the command block.
9. Push the button. (Note: The score should appear on the sign.)
10. Log out of the world.
11. Log back in to the world. (Note: The sign should now be blank.)