I believe the experiments were conductes in vaccum without light or photons. The double silt experiment I believe. From what I gather,they send particles in a controlled environment and see where they land AFTER it went through the silts, so interactions after the silt shouldn't affect which silt it goes through. That's why I said it could be some unknown interaction between the observer and the particles. Or unknown propery of a known interaction like gravitation.

To me, it sort of sounds like how time dilation works in relativity except for a different dimension.