The Bug
When observer blocks are placed then removed quickly or moved by a piston while triggered, everything that gets powered through a block will not be updated.
Ways to reproduce:
Place the observer then break it quickly. [[GIF]|http://i.imgur.com/zZtwag3.gifv]
[media]Update an observer then move it with a piston. [[IMAGE]|https://bugs.mojang.com/secure/attachment/127624/reproduce.png]
[media]
It should be noted that this also happens when moving a triggered observer with a piston, which is causing issues in flying machines.
Ways to reproduce:
[media][media]This issue will heavily affect flying machines as the pulse appears longer than it actually is because of the missing update and the piston moves back the blocks in front instead of leaving them behind (as it would if it wouldn't move the observer).
(@unknown Aww.. I made a duplicate 😞 To be fair, you created this issue while I was typing it as well 😛)