So I had strong reservations to acquire these knives despite their particularly attractive look and reputation of the blades until the day I visited the Opinel museum in Saint-Jean-de-Maurienne. There it was explained to me that the sleeves are treated to withstand the dishwasher; However, you must have them with the blade down to minimize the risk of infiltration between blade and handle.
After several months of near daily use and passage in the dishwasher I have not noticed alteration sleeves.
Thus reassured we have offered to our family members and friends.