If an observer block is pushed by a piston at the same time as it is sends a redstone signal, the block it would power after being pushed is stuck in the powered state until it gets a block update. If you build the structure in the first screenshot, and then place a upward facing observer on top of the redstone, the block on the right will stay powered. Also, if you build the structure in the fourth screenshot, the block below won't be powered when the observer updates until you give it a block update.
Linked issues
is duplicated by 13
MC-107471
When you push Observer block with same direction with piston, it can't trigger the second times
Resolved
MC-107474
Observer block stays in powered state when updated/pushed quickly
Resolved
MC-107524
Piston and Observer block glitch
Resolved
MC-107580
observer blog strange behavior while pushed with piston
Resolved
MC-107656
Observer Block leaves powered redstone wire
Resolved
8 more links
Erik Broes
Confirmed.. Reason is correct too. When they're updated the moment before they're pushed, they'll stay in powered state 🙂