Observer Blocks give a permanent redstone signal, not an pulse

Since yesterday my automatic sugercane farm broke. When the observer block gets an update it gives a permanet redstone signal, not just a pulse. For the Farm it means that pistons stay activated and the sugercane has no way to grow anymore. I had to remove the observer block to reset the pistons. By removing and replacing just a redstone dust the issue couldent be fixed since the observer block was still giving the permanent redstone signal.