Editing a sign in single player no longer pauses the game

Unlike in previous versions, editing a sign doesn't pause the game in the background in single player.

Steps to Reproduce:

• Open (or create) a single player world
• Make the setup as shown in the video attachments
• While facing the setup, press escape
  • Piston should freeze, indicating the game has paused
• Press escape again or click "Back to Game" button to return to game
• While still facing the setup, place a sign
• Take note as to whether the piston freezes, indicating if the game paused or not 
  • Observed: game resumes in background
  • Expected: game would pause in background