Placing blocks on updating blocks deletes the block and gives it back to you

If you try to place a block on a block that is updating (like an observer that is detecting something) Sometimes It will delete the block and give it back to you.

Steps to reproduce:

1. Make an observer clock (place two observers that are continuously detecting each other)
2. Take any block and try to place it on the observers
3. Notice that sometimes it won't let you place the block on the observers

Note: This happens more often on multiplayer worlds and affects both creative and survival