oh, my apologies, i never got to the final valve and thought the level ended earlier with a dead end, now i see it!
it turns out i have a fancy 180hz monitor and the game physics are tuned for 60hz and break at higher refresh rates, so the really long jumps don't work unless i switch the monitor to 60hz.
and yeah of course, that made me chuckle when i first saw it, it was so unexpected! by the way, have you seen this sign?