Lit observers no longer send block updates when moved by a piston

When a powered observer is moved by a piston, it should send block updates around the block it is facing so that any block it is strongly powering depowers. This no longer happens.

This will cause many things that uses observers moved by pistons to break; blocks being powered by the observer will be left in an invalid state where they are on but not powered.

 

How to reproduce:

Build the device shown in the first image and click the note block. The redstone lamp will stay on even though it is no longer powered.