uhh no, observers can detect string activating, (as it is in the f3 screen with 'Powered: true/false') even without tripwire, and is used in many different redstone creations, its the observer itself, it also happens with blocks too.
this has not been resolved.
proof of it not working, even with blocks: https://gyazo.com/2301c6a1a8a3078e2586e4f034c88464
the observer wont power the comparators when detecing the string (string is blue cause of my texture pack)
how i was trying to use the observer was to power a pulse extender directly, and the comparators dont detect that, and remain unpowered, and repeaters with 1 tick delay dont detect it either, though the repeaters with a 2+ tick delay do detect it, pistons and such work as normal, might be a bug with the fix for 0 tick farms
also i straight up say it was string
reopen this, it is not resolved.