While editing a non-hanging sign (right-click or when placing), the text entered is not saved if the menu is forcibly closed in some instances.

Reproduce:

1. Make a setup such that you are teleported far enough away (i.e. far enough to close the sign GUI) shortly after editing a sign
2. Place a normal sign, activate the redstone, right click the sign, and type something
3. When you get back after being teleported, you'll see that the text is not saved

This behavior is not present with the hanging signs. The text is preserved on those.