The French Air Service War Chronology 14-18 has Pilot Cpl Maxime de Verrier and Gunner Sol Lattard listed as MIA on 26.5.15. Unfortunately machine type is not mentioned and their unit is given as GB 3, not GB 1, so these casualties may of course not be related to the above incident.
Also no mention of who was responsible for the above men’s demise. No Voisins are mentioned by name on this date.