Observers sometimes don't produce pulse signals when placed together

sometimes observers don't produce pulse signals when pushed together by pistons. To reproduce, get these blocks:

2 observers

11 redstone dust

1 sticky piston

2 solid blocks (I used white concrete)

1 redstone lamp

build the contraption like provided below, and put a redstone dust in the middle of the two observers. There, you get two inactive observers.

comparison between regular and bugged on the left.

Edit: Maybe this is WAI, but I really don't get why the observers don't observer the other observing observer. When i place the redstone, they both update, and when the piston pushes, they should both get updated again. Is it because it happens too fast that they don't update?