My understanding of the delayed choice experiment is that causality is preserved only because you can't actually determine the result of a single event without comparing the two results. It's spooky action at a distance, except it's temporal instead of spatial distance.

Which honestly I find to be pretty flimsy reasoning. It's almost ontological: causality is preserved because we can't prove that it isn't.

I know it's more complex than that, but it still feels like papering over a hole in our theories.