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I just became aware of this thread and I'm not going to go back and comment on all the discussion points that have been made before, except to say: The original code which did not use a shift register was wrong, but happened the work because of a bug in the LabVIEW inplaceness algorithm. Any input tunnel should retain its original value of every iteration of the loop, so it should've stayed not-a-refnum every time, and therefore the dynamic registration should should have been lost where the loop iterated. The issue was that the left dynamic registration terminal (which is always in-place to the right one) was also in-place to the input tunnel, causing its value to be stomped incorrectly. This is clearly a bug and needed to be fixed. It violated dataflow 'rules' for how tunnels are supposed to behave, and could've made some correct programs yield incorrect behavior. This is not a change that would break a correctly written program, so it does not qualify as an "API breaking" change; this usage has always been wrong but happened to work due to a bug. (This is categorically different than changing behavior of correct code or even changing undocumented behavior, which we try strenuously to avoid.)