Not measurable mass. Therefore it doesn’t seem that special relativity is violated. Like another poster has stated, quantum mechanics states that it is possible that the photon was observed in both prisms simultaneously.
Or maybe one of their clocks was off by a millisecond or so.
The real test for this will be reproducibility.
Fine, given that photons are bosons, that's a nice pun... :-)
Q. Do Bose-Einstein statistics violate Occam's razor?
A. Only if some of the photons are superfluous. ("needlessly" multiplying entities...)
Cheers!