String still powered when no mobs/entities are triggering it

String still powered when no mobs/entities are triggering it. This bug happens both with the string alone and with the  tripwire hook.

I expected the string to activate only when a mob/entity passes through it, instead it always remains powered. The string is in front of a observer, so it not be triggered and it not activate the pistons and the rest of the farm

The string remains powered all the time. This bug happened only for a string, not for all of my strings in my world

I've placed a string in front of a observer, and the string still powered all of the time