I know it is not specefic, but take a look at the three new types of Command Blocks. They are very nice, but they are often bugging such as:
When you toggle the previous output on OFF (O) and you open the command block again, there creates a bar and deletes it again.
When you type something in the Command Block and after that you resize the window, the text that you typed is gone...
Duplicate of MC-258 and MC-89087.